Method and apparatus to detect transponder tagged objects, for example during medical procedures

ABSTRACT

The presence or absence of objects (e.g., medical implements, medical supplies) tagged with transponders may be determined in an environment in which medical procedures (e.g., surgery) are performed via an interrogation and detection system which includes a controller and a plurality of antennas positioned along a patient support structure. The antennas may, for example, be positioned along an operating table, bed, a mattress or pad or a sheet and may be radiolucent. Respective antennas may successively be activated to transmit interrogation signals. Multiple antennas may be monitored for responses from transponders to the interrogation signals. For example, all antennas other than the antenna that transmitted the most recent interrogation signal may be monitored.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/462,734 filed May 2, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/606,688 filed Oct. 27, 2009, which claimsbenefit under 35 U.S.C. 119(e) to U.S. Provisional Patent ApplicationSer. No. 61/109,104 filed Oct. 28, 2008; U.S. Provisional Patentapplication Ser. No. 61/222,443 filed Jul. 1, 2009; and U.S. ProvisionalPatent Application Ser. No. 61/242,704 filed Sep. 15, 2009, all of whichare incorporated herein by reference in their entireties.

BACKGROUND

Technical Field

This disclosure generally relates to the detection of the presence orabsence of objects tagged with transponders, which may, for example,allow the detection of medical supplies, for instance surgical objectsduring surgery.

Description of the Related Art

It is often useful or important to be able to determine the presence orabsence of an object.

For example, it is important to determine whether objects associatedwith a medical procedure, for instance a surgery or child birthdeliveries, are present in a patient's body before completion of themedical procedure. Such objects may take a variety of forms used inmedical procedures. For example, the objects may take the form ofinstruments, for instance scalpels, scissors, forceps, hemostats, and/orclamps. Also for example, the objects may take the form of relatedaccessories and/or disposable objects, for instance sponges, gauzes,and/or absorbent pads. When used in surgery, failure to locate an objectbefore closing the patient may require additional surgery, and in someinstances may have serious adverse medical consequences. In othermedical procedures, such as vaginal child birth deliveries, failure toremove objects, for instance gauze or absorbent pads can lead toinfections.

Some hospitals have instituted procedures which include checklists orrequiring multiple counts to be performed to track the use and return ofobjects during surgery. Such a manual approach is inefficient, requiringthe time of highly trained personnel, and is prone to error.

Another approach employs transponders and a wireless interrogation anddetection system. Such an approach employs wireless transponders whichare attached to various objects used during surgery. The interrogationand detection system includes a transmitter that emits pulsed widebandwireless signals (e.g., radio or microwave frequency) and a detector fordetecting wireless signals returned by the transponders in response tothe emitted pulsed wideband signals. Such an automated system mayadvantageously increase accuracy while reducing the amount of timerequired of highly trained and highly compensated personnel. Examples ofsuch an approach are discussed in U.S. Pat. No. 6,026,818, issued Feb.22, 2000, and U.S. Patent Publication No. US 2004/0250819, publishedDec. 16, 2004.

Commercial implementation of such an automated system requires that theoverall system be cost competitive and highly accurate. In particular,false negatives must be avoided to ensure that objects are notmistakenly left in the patient. Some facilities may wish to install asingle interrogation and detection system in each surgery theater orroom in which medical procedures are conducted, while other facilitiesmay move an interrogation and detection system between multiple surgicaltheaters or other rooms. In either case, the overall system will requirea large number of transponders, since at least one transponder iscarried, attached or otherwise coupled to each object which may or willbe introduced into a patient or subject during the medical procedure.Consequently, the transponders must be inexpensive. However, inexpensivetransponders typically have a relatively large variation in thefrequency of signals they emit, making it difficult to accurately detectthe signals returned by the transponders. This may be particularlydifficult in some environments which are noisy with respect to theparticular resonant frequencies of the transponders. Rooms in hospitalsin which medical procedures are performed tend to have increasinglylarger amounts of electronic equipment, and hence are becomingnotoriously noisy environments. Consequently, a new approach todetection of the presence and absence of transponder that facilitatesthe use of inexpensive transponders is highly desirable.

BRIEF SUMMARY

An apparatus to detect transponder tagged objects which are used inperforming medical procedures may be summarized as including a pluralityof antennas, at least some of the antennas spaced at intervals along atleast a portion of a length of a patient support structure that is sizedto support a patient; and a control system communicatively coupled tothe antennas and configured to successively transmit an interrogationsignal via respective ones of at least two of the antennas and tomonitor at least the other ones of the antennas for a response to theinterrogation signal in a period following the transmission of theinterrogation signal and preceding a transmission of anotherinterrogation signal. The plurality of antennas may include at leastthree antennas and each of the antennas may include a respective antennacoils, a portion a projected area of each successive one of the antennacoils along the portion of the length of the patient support structureoverlapping a portion of a projected area of at least one neighboringone of the antenna coils. The plurality of antennas may include at leastsix antennas. The control system may be configured to successivelytransmit an interrogation signal from all of the antennas in theplurality of antennas, one at a time, and to monitor all of the antennasin the plurality of antennas for a response to each of the interrogationsignals. The control system may be configured to successively transmitan interrogation signal from all of the antennas in the plurality ofantennas, one at a time, and to monitor all of the antennas in theplurality of antennas for a response to each of the interrogationsignals except the antenna from which a most recent interrogation signalwas transmitted. The control system may be configured to monitor a levelof noise, successively transmit an interrogation signal from each theantennas, one at a time, and to monitor all of the antennas for aresponse to the interrogation signal, determine which of the antennasreceives a strongest one of the responses to the interrogation signal,determine a noise estimation based on the monitored level of noise, andsubtract the noise estimation from the strongest one of the responses todistinguish a signal portion of the response signal from a noise portionof the response signal. The control system may be configured todetermine the noise estimation as an average based on the monitoredlevel of noise on all antennas except the antenna that received thestrongest one of the responses to the interrogation signals. The controlsystem may be configured to measure a level of ambient noise detectedvia a plurality of the antennas during a noise detection portion of acycle, the noise detection portion temporally spaced from any precedinginterrogation portions of the cycle such that transponders, if any, arenot responding to any electromagnetic interrogation signals transmittedduring any preceding interrogation portions of the cycle; determine aset of noise cancellation factors for each of a number of antennachannels; determine a sample averaging time for sampling noise based onthe measured level of ambient noise; determine a sample averaging timefor sampling responses to interrogation signals based on the measuredlevel of ambient noise; average noise corrected samples of noise sampledfor the determined noise sample averaging time during the noisedetection portion of the cycle; transmit a number of electromagneticinterrogation signals via one of the antennas during an interrogationportion of the cycle that follows the noise detection portion; averagenoise corrected samples of responses sampled for the determined signalaveraging time during the interrogation portion of the cycle in a periodwhile no electromagnetic interrogations signals are being transmitted byany of the antennas, the period spaced temporally sufficiently closelyto the transmission of the electromagnetic interrogations signals thatthe transponders, if any, are still responding to the electromagneticinterrogation signals; and compare averaged noise corrected samples ofresponses to the interrogation signals to at least one transponderdetection threshold.

The control system may be further configured to iterate through each ofthe antennas if averaged noise corrected samples of responses tointerrogations signals does not satisfy the at least one transponderdetection threshold.

The control system may be further configured provide a notification ofdetection of a transponder if the averaged noise corrected samples ofresponses to interrogations signals does satisfies the at least onetransponder detection threshold an N^(th) time, where N is greater than1.

The control system may be further configured to compare at least onenoise level measured from before a first interrogation portion of thecycle a noise level measured after the first interrogation portion ofthe cycle; and increase the sample averaging time for sampling responsesto interrogation signals if a result of the comparison indicates avariation in excess of a variation threshold.

The control system may be further configured to determine the set ofnoise cancellation factors for each of the number of antenna channelsby, for each respective antenna channel averaging the measured levels ofambient noise received on all the antenna channels other than therespective antenna channel for which the noise cancellation factor isbeing determined.

The antennas may be radiolucent, and may further include the patientsupport structure selected from the group consisting of: an operatingtable, a patient bed, a mattress, a pad and a sheet.

A method to detect transponder tagged objects which are used duringmedical procedures may be summarized as including for each of at leastthree antennas spaced at intervals along at least a portion of a lengthof a patient support structure, successively transmitting a number ofinterrogation signals via respective ones of the antennas; andmonitoring at least the other ones of the antennas for a response to theinterrogation signals in a period following the transmission of theinterrogation signal and before transmitting another number ofinterrogation signals via a next one of the antennas. Successivelytransmitting a number of interrogation signals via respective ones ofthe antennas may include transmitting the interrogation signals from allof the antennas, one at a time, and monitoring at least the other onesof the antennas for a response to the interrogation signals may includemonitoring all of the antennas in the plurality of antennas for aresponse to each of the interrogation signals. Successively transmittinga number of interrogation signals via respective ones of the antennasmay include transmitting the interrogation signals from all of theantennas in the plurality of antennas, one at a time, and monitoring atleast the other ones of the antenna for a response to the interrogationsignals may include monitoring all of the antennas except the antennafrom which a most recent interrogation signal was transmitted for aresponse to the most recent interrogation signal.

The method may further include measuring a level of ambient noisedetected via a plurality of the antennas during a noise detectionportion of a cycle, the noise detection portion temporally spaced fromany preceding interrogation portions of the cycle such thattransponders, if any, are not responding to any electromagneticinterrogation signals transmitted during any preceding interrogationportions of the cycle; determining a set of noise cancellation factorsfor each of a number of antenna channels; determining a sample averagingtime for sampling noise based on the measured level of ambient noise;determining a sample averaging time for sampling responses tointerrogation signals based on the measured level of ambient noise;averaging noise corrected samples of noise sampled for the determinednoise sample averaging time during the noise detection portion of thecycle; and wherein successively transmitting a number of interrogationsignals via respective ones of the antennas includes transmitting thenumber of electromagnetic interrogation signals via one of the antennasduring an interrogation portion of the cycle that follows the noisedetection portion; and monitoring at least the other ones of theantennas for a response to the interrogations signals in a periodfollowing transmission of the interrogation signal includes averagingnoise corrected samples of responses sampled for the determined signalaveraging time during the interrogation portion of the cycle in a periodwhile no electromagnetic interrogations signals are being transmitted byany of the antennas, the period spaced temporally sufficiently closelyto the transmission of the electromagnetic interrogations signals thatthe transponders, if any, are still responding to the electromagneticinterrogation signals.

The method may further include comparing averaged noise correctedsamples of responses to the interrogation signals to at least onetransponder detection threshold; and iterating through each of theantennas if averaged noise corrected samples of responses tointerrogations signals does not satisfy the at least one transponderdetection threshold.

The method may further include providing a notification of detection ofa transponder if the averaged noise corrected samples of responses tointerrogations signals does satisfies the at least one transponderdetection threshold an N^(th) time, where N is greater than 1.

The method may further include comparing at least one noise levelmeasured from before a first interrogation portion of the cycle a noiselevel measured after the first interrogation portion of the cycle; andincreasing the sample averaging time for sampling responses tointerrogation signals if a result of the comparison indicates avariation in excess of a variation threshold. Determining the set ofnoise cancellation factors for each of the number of antenna channelsmay include, for each respective antenna channel averaging the measuredlevels of ambient noise received on all the antenna channels other thanthe respective antenna channel for which the noise cancellation factoris being determined. Successively transmitting a number of interrogationsignals may include successively transmitting the interrogations signalsat a number of different frequencies at a number of different times.

An apparatus to detect transponder tagged objects which are used inperforming medical procedures may be summarized as including a patientsupport structure that is sized to support a patient; and at least threeantennas positioned along at least a portion of a length of the patientsupport structure, each of the antennas positioned along the length ofthe patient support structure radiolucent to X-ray frequencyelectromagnetic energy, and each of the antennas having a respectiverange, the ranges of the antennas in each neighboring pair of antennasat least partially overlapping. The patient support structure may beelongated having a longitudinal axis and the antennas are coil antennas,at least some of the coil antennas arranged successively along thelongitudinal axis. A portion of each successive one of the antenna coilsmay be arranged successively along the longitudinal axis of the surgicaltable with a projected area that overlaps a portion of a projected areaof at least one neighboring one of the antenna coils. The patientsupport structure may have at least one X-ray film receiving receptacleand the antennas are positioned between a patient support surface of thepatient support structure and the at least one X-ray film receivingreceptacle. The antennas may each include a respective stripe-linealuminum coil having a number of windings, each stripe-line aluminumcoil has a thickness that is not greater than 200 microns. Eachstripe-line aluminum coil may have a thickness that is not greater than100 microns.

The antennas may be carried by the patient support structure on, in orunder a patient support surface, and may further include at least onepad that overlies at least one of the antennas.

The apparatus may further include a control system communicativelycoupled to the antennas and configured to successively transmit aninterrogation signal via respective ones of the antennas and to monitorat least the other ones of the antennas for a response to theinterrogation signal in a period following the transmission of theinterrogation signal and preceding a transmission of anotherinterrogation signal.

The apparatus may further include a pedestal that supports the patientsupport structure, wherein the control system is at least partiallyhoused in the pedestal.

The apparatus may further include at least one antenna port carried bythe patient support structure, the at least one antenna portcommunicatively coupled to at least one of the antennas andcommunicatively coupleable to the control system.

The apparatus may further include at least one visual indicator carriedby the patient support structure, the at least one visual indicatorcommunicatively coupled to the control system and operable thereby toproduce visual indications indicative of responses to the interrogationsignals; and at least one user switch carried by the patient supportstructure, the at least one switch communicatively coupled to thecontrol system and operable thereby to control at least one aspect of anoperation of the control system. The patient support structure may be atleast one of a pad or a mattress that carries the antennas on at leastone of an exterior or an interior thereof, and the at least one of thepad or the mattress may include at least one communications interface toprovide selectively decoupleable communicative coupling with at leastsome of the antennas. The at least one of the pad or the mattress mayhave a compliant inner portion and an outer cover that at leastpartially surrounds the compliant inner portion and which is imperviousto bodily fluids, the compliant inner portion and the outer coverincluding radiolucent materials that can withstand multiplesterilization cycles. The patient support structure may be a sheet thatcarries the antennas on at least one of an exterior or an interiorthereof, the sheet including at least one communications interface thatprovides communicative coupling with at least some of the antennas.

The apparatus may further include a number of sensors carried by thepatient support structure, the sensors responsive to a respective forceexerted by a respective portion of the patient. Each of the sensors maybe communicatively coupled to provide a signal indicative of therespective force exerted by the respective portion of the patient.

The apparatus may further include a gel carried by the patient supportstructure at least at a number of locations that correspond to a numberof defined locations of the patient when the patient is supported by thepatient support structure.

A system may be summarized as including a transponder tag coupled to amedical supply item, the transponder tag configured to wirelesslyreceive electromagnetic energy in the form of a number of interrogationsignals and to emit a response to the interrogation signal by radiatingelectromagnetic energy; an array of antennas located in a medicalprocedure environment in which medical procedures are performed; and acontroller communicatively coupled to the array of antennas andconfigured to perform a transponder detection cycle that includes anumber of noise detection portions and a number of interrogationportions temporally spaced from the noise detection portions, duringwhich the controller: monitors at least two of the antennas of the arrayof antennas for an ambient noise in the medical procedure environmentduring the noise detection portions of the transponder detection cycle,the noise detection portions spaced sufficiently from the interrogationportions that the transponder is not emitting a response detectable bythe controller to any previous interrogation signals; emits a number ofinterrogation signals from each of at least two of the antennas of thearray of antennas, successively, during a number of transmission periodsof the interrogation portions of the transponder detection cycle; andmonitors at least two antennas for any responses to the interrogationsignals during a number of detection periods of the interrogationportions of the transponder detection cycle, the detection periodsfollowing respective ones of the transmission periods sufficientlyclosely in time that the transponder is still emitting a response to theinterrogation signals by all of the antennas in the array except onethat emitted the most recent signal. The controller may monitor at leasttwo antennas for any responses to the interrogation signals during anumber of detection periods of the interrogation portions of thetransponder detection cycle by monitoring all antennas of the antennaarray. The controller may monitor at least two antennas for anyresponses to the interrogation signals during a number of detectionperiods of the interrogation portions of the transponder detection cycleby monitoring all antennas of the antenna array except the antenna thatemitted a most recent one of the interrogation signals.

The controller may be further configured to determine a respective noiseestimation for each antenna and to compensate any responses received viathe antenna using the respective noise estimation.

The controller may be further configured to determine a respective noiseestimation for each antenna based on noise monitored on a number of theantennas of the antenna array other than the antenna for which the noiseestimation is being determined and to compensate any responses receivedvia one of the antennas using the respective noise estimation for theantenna. The antennas of the antenna array may be physically coupled toa light fixture positioned above a patient support structure. Theantennas of the antenna array may be physically coupled to the patientsupport structure. The antennas of the antenna array may be physicallycoupled to a curtain adjacent to the patient support structure.

The system may further include a hand held wand antenna communicativelycoupled to the controller to emit an number of interrogation signals andto monitor for a number of responses to interrogation signals.

An apparatus may be summarized as including at least one electricallyinsulative substrate; and a first plurality of antennas distributedalong at least a portion of the at least one insulative substrate, eachantenna comprising at least one coil with a plurality of windings andcomposed of a plurality of segments electrically coupled in series toone another, the segments of each antenna carried on at least twodifferent layers and electrically connected through at least one via,the segments on a first layer laterally spaced apart from one anotherwith respect to a longitudinal axis of the coils to form gaps betweensuccessively adjacent ones the segments on the first layer, and thesegments on at least a second layer laterally spaced apart from oneanother to form gaps between successively adjacent ones of the segmentson the second layer, the segments on the second layer located directlybelow the gaps formed between the successively adjacent ones of thesegments on the first layer. The segments may have a width and the gapsmay have a width approximately equal to the width of the segments suchthat any attenuation of electromagnetic radiation by the segments may beapproximately constant in an area enclosed between an outer perimeterand an inner perimeter of each of the antennas. Each antenna may includetwo coils, a first coil composed of segments on the first layer and thesecond coil composed of segments on the second layer, and a singleelectrical connection that electrically connects a distal end of thefirst coil to a distal end of the second coil through the at least onevia.

The apparatus may further include a controller communicatively coupledto the antennas and configured to drive the antennas to emit a number ofelectromagnetic interrogation signals to provide energy to atransponder, the controller being further configured to monitor at leastsome of the antennas for any electromagnetic responses from thetransponder to the interrogation signals.

The apparatus may further include a hand held wand antennacommunicatively coupled to the controller to emit a number ofinterrogation signals and to monitor for a number of responses tointerrogation signals. There may be from six to eight antennas in thefirst plurality of antennas. The first plurality of antennas may bearranged in a substantially non-overlapping configuration.

The apparatus may further include a second plurality of antennas spacedlongitudinally from the first plurality of antennas and which overlap atleast some of the antennas of the first plurality of antennas. There maybe from six to eight antennas in the first plurality of antennas andfrom two to four antennas in the second plurality of antennas. The atleast one electrically insulative substrate may be part of a patientsupport structure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn, are notintended to convey any information regarding the actual shape of theparticular elements, and have been solely selected for ease ofrecognition in the drawings.

FIG. 1 is a schematic diagram showing an environment in which a medicalprocedure is performed, for example a surgical environment including atable, bed or other structure to carry or support at least a portion ofa patient, that includes a plurality of antennas, and a controllercommunicatively coupled to the antennas an interrogation and detectionsystem to detect an object tagged with a transponder in a patient,according to one illustrated embodiment.

FIG. 2 a top plan view of the table, bed or other structure of FIG. 1showing the plurality of antennas, according to one illustratedembodiment.

FIG. 3 is a top plan view of the table, bed or other structure of FIG. 1showing approximate ranges of each of the antennas of FIG. 2.

FIG. 4 is a top plan view of a patient support structure showing anumber of antennas on a patient support surface and a number of antennason an opposed surface, according to another illustrated embodiment.

FIG. 5A is a side elevational view of the patient support structure ofFIG. 4.

FIG. 5B is a cross-sectional view of the patient support structure ofFIG. 4 taken along section line 6 of FIG. 4.

FIG. 6A is a top plan view of a support structure showing a number ofantennas on a patient support surface and a number of antennas on anopposed surface, according to yet another illustrated embodiment.

FIG. 6B is a cross-sectional view of the patient support structure ofFIG. 6A taken along section line 7 of FIG. 6A.

FIG. 6C is a partial isometric view of the patient support structure ofFIGS. 6A and 6B, enlarged to illustrated electrically conductive pathsor traces of the antennas.

FIG. 7 is a cross-sectional view of a patient support structure havingrecesses in which the antennas are received, according to anotherillustrated embodiment.

FIG. 8A is a top plan view of a patient support structure in the form ofa bed or an operating table showing a number of antennas arranged in anon-overlapping relationship, according to another illustratedembodiment.

FIG. 8B is a top plan view of a patient support structure in the form ofa mattress or pad showing a number of antennas arranged in anon-overlapping relationship, according to another illustratedembodiment.

FIG. 8C is a top plan view of a patient support structure in the form ofa sheet showing a number of antennas arranged in a non-overlappingrelationship, according to another illustrated embodiment.

FIG. 9 is an enlarged top plan view of an antenna according to oneillustrated embodiment, where the antenna is formed from multiple coilsof a conductive material that is radiolucent.

FIG. 10A is an enlarged top plan view of an antenna according to oneillustrated embodiment, wherein the antenna is formed of a top coil ofconductive material and a bottom coil of conductive material.

FIG. 10B is an enlarged top plan view of the top coil of the antennaFIG. 10A.

FIG. 10C is an enlarged top plan view of the bottom coil of the antennaFIG. 10A.

FIG. 10D is a cross-sectional view of a portion of a patient supportstructure carrying the top and bottom coils of the antenna of FIG. 10A,according to one illustrated embodiment.

FIG. 10E is a cross-sectional view of a patient support structure with aplurality of antennas, according to another illustrated embodiment.

FIG. 10F is a top plan view of a patient support structure comprising aplurality of antennas, according to still another illustratedembodiment.

FIG. 11 is a cross-sectional view of a portion of a patient supportstructure with an antenna carried in opposed surfaces thereof, accordingto yet still another illustrated embodiment.

FIG. 12 is a cross-sectional view of a portion of a patient supportstructure an antenna of FIG. 10A carried on opposed surfaced thereof,according to even another illustrated embodiment.

FIG. 13A is a schematic diagram showing a surgical table with aplurality of antennas and a controller positioned in a pedestal of thesurgical table, according to another illustrated embodiment.

FIG. 13B is a schematic diagram showing a bed such as a patient bed usedin an environment where medical procedures are preformed, the bedincluding a plurality of antennas and a controller positioned on a frameof the bed, according to another illustrated embodiment.

FIG. 14A is a side elevational view of an overhead light fixture for usein a medical procedure and a light shade with several antennas supportedby the light fixture, according to one embodiment in which the lightshade is shown in a retracted position or configuration of FIG. 10A.

FIG. 14B is a side elevational view of the light fixture and a lightshade in which the light shade is shown in an extended position orconfiguration.

FIG. 14C is a side elevational view of a light fixture for use in amedical procedure and a light shade with several antennas according toanother illustrated embodiment.

FIG. 15A is an isometric view of a track and a curtain or drapecontaining several antennas, according to one illustrated embodiment.

FIG. 15B is a side elevational view of a sheet containing severalantennas and configured to be hung from a support according to oneembodiment.

FIG. 16 is a schematic diagram of a controller, according to oneillustrated embodiment, including a motherboard and a plurality ofplug-in boards, one for each of the antennas.

FIG. 17 is a schematic diagram of a portion of a control system of theinterrogation and detection system, according to one illustratedembodiment.

FIG. 18 is a schematic diagram of a software configuration of theinterrogation and detection system, according to one illustratedembodiment.

FIGS. 19A-19I are an electrical schematic diagram of the interrogationand detection system including a control circuit and antenna, accordingto one illustrated embodiment.

FIG. 20 is a timing diagram illustrating a method of frequency hopping,according to one illustrated embodiment.

FIG. 21A is a timing diagram illustrating pulsed timing, according toone illustrated embodiment.

FIG. 21B is a timing diagram illustrating pulsed timing, according toanother illustrated embodiment.

FIG. 22 is a timing diagram showing activation of a pair of transistorsof the control circuit in a push-pull configuration to drive theantenna, according to one illustrated embodiment.

FIG. 23A is a flow diagram of a method of operating an interrogation anddetection system, according to one illustrated embodiment.

FIG. 23B is a flow diagram of a method of monitoring all antennas for aresponse to an interrogation signal, according to one illustratedembodiment.

FIG. 23C is a flow diagram of a method of monitoring all antennas excepta transmitting antenna for a response to an interrogation signal,according to one illustrated embodiment.

FIG. 24A is a high level flow diagram of a method of operating aninterrogation and detection system to detect transponders, according toone illustrated embodiment.

FIG. 24B is a low level flow diagram of a method of operating aninterrogation and detection system to sample noise and responses and toadjust sampling times and perform noise correction, according to oneillustrated embodiment, the method useful with the method of FIG. 24A.

FIG. 24C is a flow diagram of a method of operating an interrogation anddetection system to determine whether a transponder has been detected,according to one illustrated embodiment, the method useful with themethod of FIG. 24A.

FIGS. 25A-25F are flow diagrams of methods of operating an interrogationand detection system by measuring and/or compensating for noise,according to various illustrated embodiments, the methods useful withthe method of FIG. 24A.

FIG. 26A is a graph showing a measured or sampled response versus timewithout noise cancellation where a noise source is present but notransponder is present, according to one illustrated embodiment.

FIG. 26B is a graph showing a measured or sampled response versus timewith noise cancellation where a noise source is present but nottransponder is present, according to one illustrated embodiment.

FIG. 26C is a graph showing a measured or sampled response versusfrequency without noise cancellation where a noise source is present butno transponder is present, according to one illustrated embodiment.

FIG. 26D is a graph showing a measured or sampled response versusfrequency with noise cancellation where a noise source is present butnot transponder is present, according to one illustrated embodiment.

FIG. 27A is a graph showing a measured or sampled response versus timewithout noise cancellation where a noise source and a transponder arepresent, according to one illustrated embodiment.

FIG. 27B is a graph showing a measured or sampled response versus timewith noise cancellation where a noise source and a transponder arepresent, according to one illustrated embodiment.

FIG. 27C is a graph showing a measured or sampled response versusfrequency without noise cancellation where a noise source and atransponder are present, according to one illustrated embodiment.

FIG. 27D is a graph showing a measured or sampled response versusfrequency with noise cancellation where a noise source and a transponderare present, according to one illustrated embodiment.

FIG. 28 is an isometric view of a surgical environment including anoperating table that carries a plurality of antennas, a hand held wandantenna, and a controller according to one illustrated embodiment.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with transmitters,receivers, or transceivers and/or medical equipment and medicalfacilities have not been shown or described in detail to avoidunnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Further more, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

Many of the embodiments described herein, perform interrogation anddetection of transponder tagged objects using multiple antennas (e.g.,six antennas). Successive ones of the antennas may be used to transmitan interrogation signal, while two or more antennas are monitored for aresponse to the interrogation signal. Such may provide significantadvantages over more conventional methods, for example motion basedmethods that employ motion (e.g., sweeping) of an antenna (e.g., wand)over a patient. For instance, this allows the transmit and receive pathsto the transponder to be different from one another (e.g., transmit pathis from a first antenna to a transponder, while the receive path is fromthe transponder to a second antenna). Hence, the path length to thetransponder may be shortened in many configurations, thus improving thesignal. For instance, when using a single antenna to both transmit aninterrogation signal and to receive a response to the interrogationsignal, the power of the received signal is equal to about the 6^(th)root of the input power. However, when using multiple antennas totransmit and receive over the same area, interrogation path length inone direction may be shorter. Another advantage is that all scan time isaveraged, allowing a longer noise time averaging (e.g., 10 seconds) asopposed to motion based scanning, where integration time may be limited(e.g., about 0.25 seconds per sample). Even further, a representativevalue of noise samples measured over a plurality of antennas may beemployed to determine noise to be removed from noise plus signalsreceived at one of the antennas, thereby advantageously lowering a noisefloor and/or increasing range or performance. Thus, the variousdisclosed embodiments may provide significantly better performance.

FIGS. 1 and 2 show a medical procedure environment 10 in which medicalprocedures are performed, for example a surgical environment in whichsurgeries are performed, a patient room in which child birth deliveriesor other medical procedures are performed or a physician's office, etc.The medical procedure environment 10 includes a table (e.g., surgicaltable), bed, or other structure 12 which can carry a patient or portionthereof and an interrogation and detection system 14. The interrogationand detection system 14 includes a plurality of antennas 16 a-16 f(collectively 16, shown in broken line in FIG. 1 to indicate that suchare hidden in that view) which are carried by the patient supportsurface 12. The interrogation and detection system 14 also includes acontroller 18 communicatively coupleable to the antennas 16 by one ormore wired or wireless communication paths, for example coaxial cable20. As discussed in detail below, the interrogation and detection system14 is operable to ascertain the presence or absence of objects 22 a, 22b (collectively 22) tagged with transponders 24 a, 24 b (collectively24), which may be in or on a patient (not shown).

The table, bed or other structure 12 may include a patient supportstructure 26 and a pedestal or base 28 which supports the patientsupport structure 26. The patient support structure 26 should havedimensions sufficient to support at least a portion of a patient duringa medical procedure, for instance during surgery, child birth, etc.Hence, the patient support structure 26 may have a length of six feet ormore and a width of two feet or more. The patient support structure 26may have two or more articulated sections 26 a-26 c, as illustrated inFIG. 1 or 2, or may be a unarticulated or unitary structure asillustrated in FIGS. 4, 7 and 9. Hinges 30 a, 30 b (collectively 30) orother coupling structures may couple the articulated sections 26 a-26 c.The hinges 30 may, for example, be located along a longitudinal axis 32of the patient support structure 26 at locations that would approximatethe anticipated position of a between a patient's legs and torso andbetween the patient's torso and head.

The patient support structure 26 is preferably made of a rigid materialand is preferably radiolucent. Various radiolucent materials may beemployed, for instance carbon fiber or radiolucent plastics. Suchadvantageously allows radiological technologies to be employed, forexample X-ray imaging. For example, the patient support structure 26 maybe molded from plastics such as an acrylic or a phenolic resin (e.g.,commercially available under the trademark SPAULDITE®). In someembodiments, the patient support structure 26 may include a frame. Theframe may be made of a metal which may not be radiolucent. In suchembodiments, the frame preferably makes up a small percentage of thetotal area of the patient support structure 26. The patient supportstructure 26 may be capable of withstanding multiple cycles ofsterilization (e.g., chemical, heat, radiation, etc.). A large varietyof surgical tables, patient beds and other structures capable ofcarrying a patient or a portion of a patient are commercially available.Many of these commercially available structures include electric motorsand electronics. Typically, there is no or minimum regulation ofnon-ionizing electromagnetic radiation generated by such electric motorsand electronics. Hence, many environments 10 in which medical proceduresare performed tend to be electromagnetically noisy environments.

The table, bed or other structure 12 may include one or more mattressesor pads 34 a-34 c (collectively 34), and/or may include one or moresheets (not shown in FIG. 1 for sake of clarity of illustration). Themattresses or pads 34 and/or sheets may overlie the antennas 16. Themattresses or pads 34 may take a variety of forms, and may bedisposable, or may be capable of withstanding multiple cycles ofsterilization (e.g., chemical, heat, radiation, etc.). The mattresses orpads 34 are preferably radiolucent. The mattresses or pads 34 may take aconventional form, for example cotton, open cell or a closed cell foamrubber, with or without an appropriate cover. Alternatively, themattresses or pads 34 may include one or more bladders (e.g., dual layerurethane envelope) to receive a fluid (e.g., air, water, etc.) toselectively inflate one or more portions of the mattresses or pads 34,and/or to control a temperature of one or more portions of themattresses or pads 34. In such embodiments, the fluid should beradiolucent. The mattresses or pads 34 may include a cushioning gel orpolymer material (e.g., polymer foam). Such may alleviate pressurepoints, reducing the formation of sores or ulcers, particularly duringlong medical procedures. In such embodiments, the cushioning gel orpolymer material should be radiolucent. The cushioning layer may includerecesses or voids formed at locations selected to accommodate apatient's anatomy. The mattresses or pads 34 may be detachably securedto the patient support structure 26 via various fasteners, for instanceties, or hook and loop fastener commonly available under the trademarkVELCRO®.

The pedestal or base 28 may be fixed, or may be moveable. The pedestalor base 28 may include one or more actuators (e.g., motors, pumps,hydraulics, etc.) and/or drive mechanisms (e.g., gears, mechanicalcouplings) or linkages (not shown) that allow a position and/ororientation of the patient support structure 26 to be adjusted. Forexample, the pedestal or base 28 may telescope to allow the patientsupport structure 26 to be mechanically raised and lowered. Also forexample, the pedestal or base 28 may allow the patient support structure26 to be mechanically tilted or rotated about an axis that isperpendicular to a patient support surface 37 of the patient supportstructure 26.

As illustrated, portions of one or more of the antennas 16 may overlap.For example, where the antennas are coil antennas, each formed of one ormore coils, a portion of an area enclosed by an outermost coil of eachantenna 16 may overlap a portion of an area enclosed by an outermostcoil of a neighboring antenna 16. The area enclosed or enclosed area maybe an area enclosed by a normal or perpendicular projection of aperimeter defined the outermost coil of the respective antenna 16. Insuch embodiments, neighboring antennas 16 may be electrically insulatedfrom one another by one or more electrically insulating layers orsubstrates. For example, successively adjacent antennas 16 may becarried one opposite surfaces (e.g., opposed outer surfaces, or multipleinner surfaces, or one or more outer and inner surfaces) of a singlesubstrate. As discussed in more detail below, the antennas mayadvantageously be radiolucent, for example being formed of a radiolucentmaterial (e.g., substantially transparent to X-ray or Gamma rayradiation) or a material that at a thickness employed is substantiallyradiolucent. For example, an electrically conductive trace of aluminumhaving a thickness of 200 microns or less sufficiently passes X-rays tobe considered radiolucent. More preferably, an aluminum trace having athickness of 30 microns sufficiently passes X-rays such that even astack or overlapping portions of three coils (combined thickness under100 microns) to be radiolucent. An antenna may be considered radiolucentif it is not detectable by an radiologist in an X-ray produced via 10 kVto 120 kV X-ray machine, or preferably a 40 KV X-ray machine inconjunction with a standard 12 inch X-ray image intensifier. An antennamay be considered radiolucent if a coil includes thirty turns orwindings and is not detectable by an radiologist in an X-ray.

The patient support structure 26 may include one or more film receivingreceptacles 29 (only one called out in FIG. 1). The film receivingreceptacles 29 may be spaced relatively below a patient support surface37 of the patient support structure 26. The film receiving receptacles29 are sized, dimensioned and/or positioned to receive film, for exampleX-ray film. The film receiving receptacles 29 my be sized and/ordimensioned to receive a film tray or other film holder (notillustrated) which holds the film. Along with the use of radiolucentmaterials, such advantageously allows a patient X-ray images or otherradiological images of the patient to be produced, generated or made,while the patient is supported by the patient support structure 26. Asused herein an in the claims, the term radiolucent means substantiallytransmissive to energy in the X-ray portion of the electromagneticspectrum, that is passing sufficient X-ray energy to produce an X-rayimage at standard power levels and standard conditions employed inconventional medical imaging.

The table (e.g., surgical table), bed or other structure 12 may includean interrogation and detection system interface 36. The interrogationand detection system interface 36 may include one or more communicationsports 38 that allow communicative coupling to be selectively ordetachably made between the antennas 16 and the controller 18. Suchcommunications ports 38 may, for example, take the form of coaxialconnectors, or other communications connectors. Interrogation anddetection system interface 36 may include one or more output devices toprovide indications to a user. For instance, the interrogation anddetection system interface 36 may include one or more visual indicators40 (only one called out in FIGS. 1 and 2) to provide indications of apresence and/or an absence of an object. Such may also provide a visualindication that is indicative of a status of a scanning operation by theinterrogation and detection system 14, for instance scanning started,scanning completed, and/or occurrence of an error condition. The visualindicators 40 may take a variety of forms, for example light sources ofone or more colors. Light sources may include incandescent lights, lightemitting diodes (LEDs), organic light emitting diodes (OLEDs), and/orliquid crystal displays (LCDs). Also for instance, the interrogation anddetection system interface 36 may include one or more aural indicators42 to provide aural indications of a presence and/or an absence of anobject and/or a status of a scan operation or occurrence of an errorcondition. The aural indicator 42 may, for example, take the form of oneor more speakers. The interrogation and detection system interface 36may include one or more switches 44 that allow input to be provided tothe controller 18. Switches 44 may, for example, allow a user to turn ONthe interrogation and detection system 14, start a scan operation, stopa scan operation, adjust a sensitivity of the scanning, adjust one ormore frequencies, select or adjust an output type (e.g., type of visualalert, type of aural alert) or level (e.g., brightness, sound level orvolume, etc.).

The objects 22 may take a variety of forms, for example instruments,accessories and/or disposable objects useful in performing medicalprocedures, for example surgical procedures, child birth deliveryprocedures, and/or other medically related procedures. For instance,some objects 16 a may take the form of scalpels, scissors, forceps,hemostats, and/or clamps. Also for example, some objects 22 b may takethe form of sponges (e.g., surgical sponges), gauze and/or padding. Theobjects 22 are tagged, carrying, attached or otherwise coupled to arespective transponder 24. Some embodiments of the interrogation anddetection system 14 disclosed herein are particularly suited to operatewith transponders 26 which are not accurately tuned to a chosen orselected resonant frequency. Consequently, the transponders 24 do notrequire high manufacturing tolerances or expensive materials, and thusmay be inexpensive to manufacture.

Transponders 24 may include a miniature ferrite rod with a conductivecoil wrapped about an exterior surface thereof to form an inductor (L),and a capacitor (C) coupled to the conductive coil to form a series LCcircuit. The conductive coil may, for example, take the form of a spiralwound conductive wire with an electrically insulative sheath or sleeve.The transponder 24 may include an encapsulation that encapsulates theferrite rod, conductive coil, and capacitor. The encapsulant may be abio-inert plastic, that protects the ferrite rod, conductive coil and/orcapacitor from pressure and/or from fluids, for example bodily fluids.In some embodiments, the ferrite rod may include a passage sized toreceive a physical coupler, for example a bonding tie or string. Thebonding tie or string may take the form of an elastomeric x-ray opaqueflexible elongated member, that may be used to attach the transponder 24to various types of objects 22, for example surgical sponges. Thetransponder 24 may have a length of about 8 millimeters and a diameterof about 2 millimeters. Employing such small dimensions ensures that thetransponder 24 does not impede deformation of objects 16 such assponges. The transponder 24 may include an optional diode (not shown),to protect against over-voltage occurrences caused by other electronicinstruments. The transponders 24 may be attached to hemostats, scissors,certain forms of forceps, and the like. In some embodiments, thetransponders 24 may be coupled to the object 22 by way of a clamp orholder. In some embodiments, the transponders 24 may be retained withina cavity of the holder. In some embodiments, the holder may be fashionedof a durable deformable material, such as surgical grade polymer, whichmay be deformed to clamp securely onto the finger or thumbhole of aninstrument. In other embodiments, the transponders 24 may be attached toobjects 22 by way of pouches fashioned of sheet material (e.g., surgicalfabric) surrounding the transponder 24. The transponder 24 is retainedwithin the pouch, and in some embodiments the pouch may be sewn orotherwise sealed. Sealing may be done with adhesive, hot glue, clamping,grommeting, or the like. Various embodiments of suitable transpondersand retention devices are discussed in U.S. Provisional PatentApplication No. 60/811,376 filed Jun. 6, 2006, U.S. Provisional PatentApplication No. 61/091,667 filed Aug. 25, 2008, U.S. patent applicationSer. No. 11/759,141 filed Jun. 6, 2007, U.S. patent application Ser. No.12/046,396 filed Mar. 11, 2008, U.S. Pat. No. 6,026,818 issued Feb. 22,2000, U.S. Design patent application Ser. No. 29/322,539 filed Aug. 6,2008 and U.S. Design Pat. No. D568,186 issued May 6, 2008, all of whichare incorporated herein by reference in their entireties.

In use, the medical provider 12 may use the switches 44 to cause a scanof the patient 18, for instance jut before closing during surgery, inorder to detect the presence or absence of the transponder 26, and hencean object 16.

FIG. 3 shows approximate ranges R₁-R₆ for the six antennas 16 of theembodiment of FIGS. 1 and 2.

FIG. 3 is illustrative and does not necessarily represent actual ranges.The illustrated ranges R₁-R₆ (collectively R) show that the ranges R₁-R₆are typically larger than the area of the antennas 16. Ranges R₁-R₆ maybe affected by a variety of factors, including the power of theinterrogation signal, distance between the transponders 24 and theantennas 16, and/or the sensitivity and/or impedance matching betweenthe transponders 24 and interrogation and detection system 14. Many ofthe ranges R₁-R₅ overlap neighboring ranges R₁-R₅, although in thisillustrated embodiment one range R6 does not overlap any other rangeR₁-R₅. In other embodiments, all ranges overlap. Alternatively, none ofthe ranges may overlap. Other arrangements of antennas 16 and/or rangesR, are of course possible.

FIGS. 4, 5A and 5B show a patient support structure 626, according toanother illustrated embodiment.

The patient support structure 626 may, for example, be part of a table,for instance a surgical table, part of a bed or another structuredesigned to carry a patient or portion of a patient. The patient supportstructure 626 is a non-articulated, single piece or unitary structure.While illustrated as a single, unitary construction, the patient supportstructure 626 may be formed of two or more sections, which may or maynot be articulated. The patient support structure 626 is formed as asubstrate 650 having a patient support surface 637 and an opposedsurface 652 that is opposed from the patient support surface 637. Thesubstrate 650 may be formed of one or more layers. For example, thesubstrate 650 may be a composite material. The substrate 650 may, forexample, be formed as a resin impregnated carbon fiber structure, whichmay advantageously omit any metal or ferrous metal structural elements.Alternatively, the substrate 650 may minimize the use of any metal orferrous metal structural elements and locate any metal or ferrous metalstructural elements at the peripheries of the substrate 650.

A first set of antennas 616 a, 616 c, 616 e, 616 g are positioned on thepatient support surface 637, while a second set of antennas 616 b, 616d, 616 f are positioned on the opposed surface 652. Such allowsneighboring ones of the antennas (collectively 616), or portionsthereof, to overlap, while electrically insulating each antenna 616 fromone another. While illustrated as being carried on outer surfaces of thepatient support structure 650 one or more of the antennas 616 could becarried on one or more inner layers of the patient support structure 650where the patient support structure 650 is formed of two or more layers,for instance as a laminate structure.

FIGS. 6A-6C show a patient support structure 626 and antennas 616 a-616h (collectively 616), according to another illustrated embodiment,wherein individual ones of the electrically conductive paths or tracesof the antennas 616 are visible.

The patient support structure 626 may, for example, be part of a table,for instance a surgical table, part of a bed (e.g., patient or hospitalbed) or another structure designed to carry a patient or portion of apatient on which a medical procedure may be performed. The patientsupport structure 626 is a non-articulated, single piece or unitarystructure. While illustrated as a single, unitary construction, thepatient support structure 626 may be formed of two or more sections,which may or may not be articulated. The patient support structure 626is formed as a substrate 650 having a patient support surface 637 and anopposed surface 652 that is opposed from the patient support surface637. The substrate 650 may be formed of one or more layers. For example,the substrate 650 may be a composite material. The substrate 650 may,for example, be formed as a resin impregnated carbon fiber structure,which may advantageously omit any metal or ferrous metal structuralelements. Alternatively, the substrate 650 may minimize the use of anymetal or ferrous metal structural elements and locate any metal orferrous metal structural elements at the peripheries of the substrate650.

The patient support structure 626 carries antennas 616 thereon and/ortherein. As best illustrated in FIGS. 6A and 6B, the antennas can betreated as two sets. A first set of antennas 616 a-616 f arrangedgenerally adjacent one another in an array of two rows on either side ofa longitudinal axis 630 and three columns spaced along the longitudinalaxis 630. These antennas 616 a-616 f do not overlap with one another.These antennas 616 a-616 f substantially extend the full length andwidth of the patient support structure 628. Alternatively, theseantennas 616 a-616 f may be spaced inwardly from a perimeter of thepatient support structure, for example where the range of the antennas616 a-616 f sufficiently covers the area of the patient supportstructure 626. A second set of antennas 616 g, 616 h are arrangedgenerally adjacent one another in an array of one row and two columns.These antennas 616 g, 616 h do not overlap with one another, howeverthese antennas 616 g, 616 h overlap the antennas 616 a-616 f of thefirst set when viewed from above the patient support structure 626.These antennas 616 g, 616 h enhance the overall coverage of the entirearea of the patient support structure 626 and volume spaced generallythere above.

While illustrated as being carried an upper outer surface 637 of thepatient support structure 626, one or more of the antennas 616 could becarried on a lower outer surface 652 and/or on one or more inner layersof the patient support structure 626, for instance where the patientsupport structure 626 is a laminate structure.

FIG. 6C shows one embodiment of the antennas 616, which may allowrelatively simple and low cost manufacturing, and which prevents theantennas 616 from electrically shorting one another.

In particular, each antenna may be formed as electrically conductivepaths or traces on one or more layers of an electrically non-conductiveor insulative substrate, for instance a flexible substrate of circuitboard material (e.g. FR4, Kapton). The electrically conductive path ortrace may form a coil pattern, hence a coil antenna with multiplewindings, as illustrated in FIG. 6C. Portions of the electricallyconductive path on one end or half of the substrate may be electricallycoupled to respective portions of the electrically conductive path onthe other end or half of the substrate via electrically conductivematerial received in a via that extends through a portion or all of thesubstrate. Thus, while the electrically conductive paths appear toterminate at a centerline 647 of each antenna, the electricallyconductive paths are in fact electrically coupled to adjacent portionsacross the centerline 647 by way of respective vias. Alternatively, theelectrically conductive path may have change in direction (e.g., 45degree turn), such that the electrically conductive path spiralsinwardly (or outwardly) with each half turn or half winding.Alternatively, or additionally, an electrically non-conductive orelectrically insulative material may overlie the electrically conductivepath on a lower surface or side and/or an upper surface or side of thesubstrate, to provide electrical insulation between overlyingsubstrates.

FIG. 7 shows a patient support structure 726, according to anotherillustrated embodiment.

The patient support structure 726 is formed as a substrate 750 having apatient support surface 737 and an opposed surface 752 that is opposedfrom the patient support surface 737. The substrate 750 may be formed ofone or more layers. For example, the substrate 750 may be a compositematerial. The substrate 750 may, for example, be formed as a resinimpregnated carbon fiber structure, which may advantageously omit anymetal or ferrous metal structural elements. Alternatively, the substrate750 may minimize the use of any metal or ferrous metal structuralelements and locate any metal or ferrous metal structural elements atthe peripheries of the substrate 750. While illustrated as a single,unitary construction, the patient support structure 726 may be formed oftwo or more sections, which may or may not be articulated.

A first set of antennas 716 a, 716 c, 716 e, 716 g are positioned inrespective recesses formed in the patient support surface 737, while asecond set of antennas 716 b, 716 d, 716 f are positioned in respectiverecesses formed in the opposed surface 752. Such allows neighboring onesof the antennas (collectively 716) to overlap, while electricallyinsulating each antenna 716 from one another. Such also advantageouslyspaced the antennas 716 of the first and second sets closer togetherwith respect to one another, which may produce more consistent resultsor performance between the various antennas 716. While illustrated asbeing carried on outer surfaces of the patient support structure 750 oneor more of the antennas 716 could be carried on one or more inner layersof the patient support structure 750 where the patient support structure750 is formed of two or more layers, for instance as a laminatestructure.

FIG. 8A shows a patient support structure 826A, according to anotherillustrated embodiment.

The patient support structure 826A is a non-articulated, single piece orunitary structure. While illustrated as a single, unitary construction,the patient support structure 826A may be formed of two or moresections, which may or may not be articulated. The patient supportstructure 826A may be formed of a variety of materials, for example, thematerials of the above described embodiments.

Notably, the patient support structure 826A carries a set of antennas816Aa-816Af (collectively 816A), which are positioned along alongitudinal axis 830 of the patient support structure 826A. Whileillustrated as positioned in non-overlapping fashioned, in someembodiments the antennas 816A may be positioned in overlapping fashion.While five antennas 816B are illustrated, the patient support structure826A may include a greater or lesser number of antennas 816A.Consequently, the antennas 816A may all be carried on the same outersurface (e.g., patient support surface) or inner surface or layer. Thus,may advantageously provide more consistent results or performancebetween the respective antennas 816, and/or may simply manufacturingand/or maintenance.

FIG. 8B shows a patient support structure, according to anotherillustrated embodiment.

The patient support structure takes the form of a mattress or pad 826Bwhich may, for example, be used on a table or bed when performing amedical procedure. While illustrated as an articulated structure withtwo joints or hinges 830Ba, 830Bb (collectively 830B), the mattress orpad 826B may be formed of a unitary, single piece non-articulatedstructure. The mattress or pad 826B may be reusable, and hence should becapable of withstanding repeated sterilization procedures (e.g., heat,chemical, radiation, etc.). Alternatively, the mattress or pad 826B maybe disposable after a single use. The mattress or pad 826B may be formedof a variety of materials, for example, the materials of the abovedescribed embodiments of mattresses or pads. As previously discussed inreference to mattresses or pads, the mattress or pad 826B may include anouter layer or cover 892B and an interior 890B (visible through brokenportion of outer layer 892B). The outer layer or cover 892B providesenvironmental protection to the interior 890B. The interior 890B may,for example, take the form of a conformable interior, which may be madeof any variety of materials. Suitable material may, for example, includecotton or a foam material such as a closed or an open cell foam rubberor LATEX®. Alternatively, the conformable interior may take the form ofa fluid (e.g., a liquid or a gas). The outer layer or cover 892B may bemade of cotton, nylon, rayon or other natural or synthetic materials.The outer layer or cover 892B may, for example, be impervious toliquids. For example, the outer layer or cover 892B may include one ormore layers of a rubber, LATEX®, polyvinyl chloride, plastic or othermaterial that is impervious to fluids, for example bodily fluids.

Notably, the mattress or pad 826B carries a set of antennas 816Ba-816Be(collectively 816B), which are positioned along a longitudinal axis 832Bof the mattress or pad 826B. While illustrated as positioned inoverlapping fashioned, in some embodiments the antennas 816B may bepositioned in non-overlapping fashion. While five antennas 816B areillustrated, the mattress or pad 826B may include a greater or lessernumber of antennas 816B. For example, the mattress or pad 826B may haveantennas 816 arranged in a similar fashion to that illustrated in FIGS.6A-6C. The antennas 816B may on opposite sides of a layer on or in themattress or pad 826B, or on two or more different layers on or in themattress or pad 826B. The layer or layers may be an outer surface (e.g.,patient support surface) or an inner surface or layer. The mattress orpad 826B includes an interface, such as a connector 894B, to allow theantennas 816B to be communicatively coupled to the controller 18 (FIG.1).

FIG. 8C shows a patient support structure, according to anotherillustrated embodiment.

The patient support structure takes the form of a sheet 826C. The sheet826C may, for example, be used on, over, or in conjunction with a table,bed, frame or other structure during a medical procedure. The sheet 826Cmay be formed of a unitary, single piece of material or a cloth, forexample a fabric. The cloth may, for example, be woven, knitted, felted,pressed, etc. The sheet 826C may be reusable, and hence should becapable of withstanding repeated sterilization procedures (e.g., heat,chemical, radiation, etc.). Alternatively, the sheet 826C may bedisposable after a single use. The sheet 826C may be absorbent or may beimpermeable to fluids, for example bodily fluids. The sheet 826C may beformed of a variety of materials, for example, cotton, nylon, rayon, orother natural or synthetic fibers. For example, the sheet 826C mayinclude one or more layers of a rubber, LATEX®, polyvinyl chloride,plastic or other material that is impervious to fluids, for examplebodily fluids.

Notably, the sheet 826C carries a set of antennas 816Ca-816Ce(collectively 816C), which are positioned along a longitudinal axis 832Cof the sheet 826C. While illustrated as positioned in overlappingfashioned, in some embodiments the antennas 816C may be positioned innon-overlapping fashion. While six antennas 816C are illustrated, thesheet 826C may include a greater or lesser number of antennas 816C. Forexample, the antennas 816 may be arranged on the sheet 826 in anidentical or similar fashion as illustrated in FIGS. 6A-6C. The antennas816C may be on opposite sides of the sheet 826C, or on two or moredifferent layers of the sheet 826C. The layer or layers may be an outersurface (e.g., patient support surface) or an inner surface or layer.The sheet 826C includes an interface, such as a connector 894C, to allowthe antennas 816C to be communicatively coupled to the controller 18(FIG. 1).

FIG. 9 shows an antenna 916, according to one illustrated embodiment.The antenna 916 may, for example, be suitable for use in any of thepreviously described embodiments.

The antenna 916 may, for example, take the form of an annulus orair-coil formed of coils of conductive material. The conductive materialmay, for example, take the form of wire or may take the form of aconductive trace printed or otherwise deposited on an inner layer or anouter surface 952 of a substrate 950. In one embodiment, the antenna 916includes ten turns evenly spaced between an inner diameter of about 11inches and an outer diameter of about 14 inches. The antenna 916 acts asan inductor. While being formed of a conductive material, the antenna916 is preferably formed of a radiolucent material. For example, theantenna 916 may be formed as a thin (e.g., thickness, width) strip linealuminum antenna.

The antenna 816 includes a pair of terminals 854 a, 854 b that provideelectrical coupling to the controller 18 (FIG. 1), for example via theports 38 of interrogation and detection system interface 36 (FIGS. 1 and2) and the coaxial cable 20.

FIGS. 10A-10C illustrate a coil antenna 1016 according to oneembodiment.

The coil antenna 1016 comprises a top coil 1017 (illustrated inisolation in FIG. 10B) and a bottom coil 1019 (illustrated in isolationin FIG. 10C). The top and bottom coils 1017, 1019 are carried by thepatient support surface 26, the top coil 1017 carried on one layer 1021a and positioned relatively above the bottom coil 1019 carried onanother layer 1021 b. The top coil 1017 is electrically coupled to thebottom coil 1019, for example, by a plug of electrically conductivematerial 1015 in a via. In practice the via connecting the top coil 1017to the bottom coil 1019 may comprise a vertical connector of the samematerial as the coils 1017, 1019. Any suitable conductor may be used toconnect the top coil to the bottom coil at the via point. In addition tobeing offset from each other vertically along a longitudinal axis 1018of the coils (see FIG. 10D), the individual windings of the two coilsare also offset from each other laterally along two perpendicular axesin a horizontal plane (La, the plane of the drawing sheet FIG. 10A) thatis perpendicular to the longitudinal axis. The layers 1021 a, 1021 b maybe opposed outer surfaces of an electrically insulative substrate, oneor more inner surfaces of the electrically insulative substrate, or acombination thereof. The electrically insulative substrate may be aunitary part of the patient support surface, integral part of thepatient support surface or attach or carried by the patient supportsurface.

FIG. 10D shows the coil antenna 1016 carried by a patient supportstructure 26, according to one illustrated embodiment.

Top coil 1017 is positioned relatively above the bottom coil 1019 in aninterior of the patient support structure 26. As noted above, the bottomcoil 1019 is offset from the top coil 1017 vertically along alongitudinal axis 1018 as well as laterally in a horizontal plane whichis perpendicular to the longitudinal axis 1018. The individual windings1021 of the top coil 1017 are spaced apart leaving gaps between eachwinding 1021. The individual windings 1023 of the bottom coil 1019 arespaced directly below the gaps between the windings 1021 of the top coil1017. The windings 1021, 1023 are thus spread in such a way to provide amore even distribution of radiolucence. This distribution of thewindings 1021, 1023 may smooth the contrast that could appear in aradiological image (e.g., X-ray image). FIG. 10D illustrates anembodiment in which the windings 1023 are spaced directly below the gapsbetween windings 1021 without overlapping the windings 1021 in a lateraldirection in the horizontal plane. In other embodiments the windings1023 may instead slightly overlap the windings 1021. In some embodimentsthe windings 1021, 1023 may cross over each other although suchcrossings may have an adverse effect on radio transparency. Many otherconfigurations of the coils 1017, 1019 and the windings 1021, 1023 willbe apparent to those of skill in the art and fall within the scope ofthis disclosure. The configuration of windings illustrated in FIG. 10Dare given only by way of example and do not limit the scope of thedisclosure. The patient support structure 26 and antenna 1016 are notdrawn to scale. Relative heights, widths, and separations of the patientsupport structure 26 and antenna coils 1017, 1019 may be different inpractice than what is shown in FIG. 10D.

This design may minimize interference with radiological imagery sources(e.g., X-rays, CAT scans, MRIs) which may be employed while a patient ison the patient support structure 26. Radiological imaging is commonlyemployed while patients are on the patient support structure 26, forexample during surgery. This may, for example, be performed bypositioning an X-ray machine above the patient support structure 26 andpositioning an X-ray sensitive film below the patient support structure26. An X-ray image is formed by exposing the film to the X-rays throughthe patient and patient support structure 26. Any object or materialthat absorbs or reflects X-rays more than its surroundings will cause anarea of contrast in the developed X-ray image. Thus, portions of thepatient support 26 structure that absorb more or less than otherportions of the patient support structure 26 will appear as a high levelof contrast in the developed X-ray image. This can make it difficult tointerpret the X-ray image. For this reason it may be beneficial tospread the coils of an antenna, even where nominally radio transparentto reduce the contrast which the antenna may otherwise cause in an X-rayimage. A coil antenna with many windings which are stacked or layeredare above others may produce a relatively high contrast and appear in anX-ray image even if a single layer of coil is nominally radiotransparent. A coil whose windings are spread apart, spread laterallyfrom one another, may also produce relatively large changes in contrast,even where nominally radio transparent. As disclosed herein, thewindings of the coils are positioned to be in adjacent non-overlappingrelationship to one another when viewed along the longitudinal axis1018. Such creates an area having a very uniform distribution of antennamaterial, and hence a very uniform radiological attenuation distributionacross that area. Such advantageously may cause any attenuation to beuniform, reducing the antenna's effect on the radiological image.

FIGS. 10E and 10F show a patient support structure 26 according to oneembodiment.

The patient support structure carries six antennas 1016 a-1016 f. Eachof the antennas 1016 a-1016 f may be similar or identical in form to theantenna 1016 illustrated in FIG. 10A-10D. The antennas 1016 a-1016 f arepositioned to provide little or no gap between antennas in the lateraldirections of the horizontal plane of the patient support surface 26,while not overlapping. As described above, this configuration may helpto reduce areas of sharp contrast in radiological images. FIG. 10E showsthe antennas 1016 a-1016 f embedded within the patient support structure26. Of course the antennas 1016 a-1016 f may not actually be visiblefrom a top view of the support structure 26. However, FIG. 10F shows theantennas 1016 a-1016 f from the top view to illustrate the relativepositions of the antennas 1016 a-1016 f. The number and configuration ofcoils, as well as the number and configuration of the winding formingthose coils, shown in FIG. 10F is not meant to be limiting. In practicethere may be a greater or lesser number of coils and/or a greater orlesser number of windings. In practice, the windings are typically notindependent loops, but are illustrated as such in FIG. 10F for ease ofillustration.

FIG. 11 shows a patient support structure carrying an antenna 1116,according to another illustrated embodiment.

The antenna 1116 comprises a top coil 1117 and a bottom coil 1119 aspreviously described. The top coil 1117 comprises windings 1121, whilethe bottom coil comprises windings 1123. The windings 1121, 1123 arelaterally offset from each other in two perpendicular directions in ahorizontal plane that is perpendicular to a longitudinal axis of theantenna 1116. The top coil 1117 is formed adjacent to and below a topsurface 1137 of the support structure 26, for example in a channel orrecess formed in the top section 1137. The bottom coil 1119 is formedabove and adjacent to a bottom surface 1152 of the support structure 26,for example, in a channel or recess formed in the bottom section 1152.

FIG. 12 illustrates a patient support structure that carries an antenna1126, according to yet another illustrated embodiment. The antenna 1216comprises a top coil 1217 and a bottom coil 1219. The top coil 1217comprises windings 1221, while the bottom coil comprises windings 1223.The windings 1221, 1223 are laterally offset from each other in ahorizontal plane that is perpendicular to a longitudinal axis of theantenna 1216. The top coil 1217 is carried directly on a top surface1237 of the support structure 26. The bottom coil 1219 is carrieddirectly on a bottom surface 1252 of the support structure 26. The topand/or bottom coils 1217, 1219 may be adhered or otherwise physicallycoupled to the respective surfaces 1237, 1252. The relative dimensionsof the features shown in FIG. 12 may not be accurate. For instance, theantenna windings 1221, 1223 may not, in practice, protrude from thesurfaces 1237, 1252 to the same extent as illustrated. Many otherconfigurations for the antennas are possible and the precedingembodiments are given only by way of non-limiting example.

FIG. 13A shows a surgical environment 1310 that includes a surgicaltable 1312 and an interrogation and detection system 1314, according toanother illustrated embodiment. The embodiment of FIG. 13A is similar insome respects to one or more of the previously described embodiments,hence only significant differences in structure and operation will bediscussed.

The surgical table 1310 may include a patient support structure 1326 anda pedestal or base 1328. The patient support structure 1326 may be alaminate structure having multiple layers. Alternatively, the patientsupport structure 1326 may be a shell type structure or housing havingan open interior. Alternatively, the patient support structure 1326 maybe a solid structure, for example a roto-molded structure.

The plurality of antennas 1316 a-1316 f (collectively 1316) of theinterrogation and detection system 1314 are carried by the surgicaltable 1312, for example carried by inner layers of the patient supportstructure 1326 or positioned in an interior of a shell or housingforming the patient support structure 1326. While illustrated as beingin overlapping relationship, in some embodiments the antennas 1316 maynot overlap. The controller 1318 of the interrogation and detectionsystem 1314 may be positioned in the pedestal or base 1328, for examplein an interior 1330 of the pedestal or base 1328. One or more wired orwireless communication paths may communicatively couple the controller1318 to the antennas 1316 and/or to an interrogation and detectionsystem interface 1336, for example coaxial cable 1320.

The interrogation and detection system 1314 may receive power for avariety of sources, for example from a wall outlet or receptacle via aconventional power cord and plug 1332.

The antennas of the interrogation and detection system 14 are notlimited to being implemented in a patient support structure 26. Previousembodiments have, by way of example, described various ways ofimplementing antennas within a patient support structure. Theseembodiments have been given purely by way of example and are notintended to be limiting. Those of skill in the art will recognize thatthe antennas may be implemented in many configurations throughout theenvironment in which medical procedures are performed.

FIG. 13B shows an environment in which medical procedures are performed1340 that includes a bed (e.g., patient bed) 1342 and an interrogationand detection system 1344, according to another illustrated embodiment.The embodiment of FIG. 13B is similar in some respects to one or more ofthe previously described embodiments, hence only significant differencesin structure and operation will be discussed.

The environment 1310, may for example, take the form of a hospital room,clinic room, or examination room of a medical practitioner's office.

The bed 1342 may include a patient support structure 1346 and a frame orbase 1348. The patient support structure 1346 may support one or moremattresses, for example a segmented mattress 1347. The frame 1348 may bemade of plastic, metal, composite, reinforced composited, and/orroto-molded materials. Various commercially available designs of framesfor patient beds are suitable. The frame 1348 may include a set ofwheels 1350 (only one called out in FIG. 13B) allowing the bed 1342 tobe easily moved. The frame 1348 may include one or more rails 1352,which may, or may not, be removable or which may, or may not, fold down.

The bed 1342 may include one or more electric motors 1354 (only onecalled out in FIG. 13B) and linkages 1356 (only one called out in FIG.13B) which are selectively actuated to move or articulate portions ofthe bed 1342 or mattress 1346. Other mechanisms may be used to moveportions of the mattress 1346. Commercially available patient orhospital beds 1342 typically include one or more pieces of electrical orelectronic equipment (e.g., electric motors 1354) which are sources ofradio noise which may interfere with the interrogation and detectionsystem 1344. Such equipment typically produce very consistent orperiodic (i.e., non-random) noise. Some embodiments of the interrogationand detection system 1344 discussed herein employ various techniques toaddress such non-random noise.

The interrogation and detection system 1344 includes a plurality ofantennas 1366 a-1366 f (collectively 1366) of the interrogation anddetection system 1344 are carried by the patient support structure 1346,mattress 1347 or frame 1348. For example, the antennas 1366 may becarried by inner layers of the mattress 1347 or positioned in aninterior of a shell or housing forming the patient support structure1346. While illustrated as being in non-overlapping relationship, insome embodiments the antennas 1366 may overlap. A controller 1368 of theinterrogation and detection system 1344 may be carried by the frame orbase 1348. One or more wired or wireless communication paths maycommunicatively couple the controller 1368 to the antennas 1366 and/orto an interrogation and detection system interface, for example coaxialcable 1370.

The interrogation and detection system 1314 may receive power for avariety of sources, for example from a wall outlet or receptacle via aconventional power cord and plug (not shown in FIG. 13B).

In some embodiments, antennas, for instance antennas 1316, 1366 (FIGS.13A, 13B, respectively) may form strain sensors as part of a straingauge. For example, the antennas may be carried by flexible substrate,for instance a flexible printed circuit board such as a polyimide(Kapton®) or polyester (Mylar®) printed circuit board. The resistance ofthe antenna varies as the substrate flexes. The change in resistance maybe measured to determine strain, and hence force applied. The antennasmay be configured and coupled in groups of fours to form full Wheatstonebridges. The antennas may additionally, or alternatively, be orientedalong various axes or dimensions to detect strain in differentdirections. Multiple layers of antennas may be employed to detect flexin two opposite directions, normal to the plane of the substrate.Alternatively, dedicated strain sensors or gauges may be employed, whichdo not function as antennas. Sensing strain may be useful in detectingexcessive and/or prolonged pressure asserted between a patient and thepatient support surface. Excess and/or prolonged pressure may cause thepatient to develop “bed sores” or ulcers. Tracking or monitoringpressure may allow the medical care provider to intervene before the“bed sores” or ulcers occur. Thus, the control system may be configuredto provide an warning or alert (e.g., visual, aural and/or tactile) whenpressure or strain exceeds some threshold in amplitude and/or time. Thecontrol system may additionally, or alternatively, provide an indicationof a position or location on the patient support surface or patientwhere the excessive pressure is occurring.

Additionally, or alternatively, one or more dedicated force sensors(e.g., strain or pressure sensors) 1367 a-1367 c (collectively 1367) maybe carried by the bed 1342. The sensors 1367 may be located at definedlocations where portions of a patient typically experience a highpressure or force. Bed sores or ulcers commonly develop at these areas.While, the precise locations may vary dependent on the size of a patientand/or specific position of a patient in the bed, one or more sensors1367 may be distributed about areas where specific portions (e.g., hips,buttocks) of a patient would typically be located when on the patientsupport structure.

FIG. 14A shows a number of antennas 1416 carried by a lightshade 1432 ofa light fixture 1434 used in medical procedures, according to oneillustrated embodiment, in which the lightshade is shown in a retractedor undeployed position or configuration. The light fixture 1434 mayhouse one or more lights to be used during surgery, birth delivery orother medical procedure, including dental procedures. During a medicalprocedures such as surgery, the patient laying on a patient supportstructure is typically illuminated brightly by an overhead light fixture1434. The light fixture 1434 may be situated directly above theoperating table or slightly offset as desired. The light fixture 1434 isalso generally positioned as close to the patient as possible withoutimpeding the medical services providers (e.g., surgeons and staff)during the medical procedure (e.g., surgery, birth delivery). Theproximal overhead position allows the light fixture 1434 to brightlyilluminate the patient. The light fixture 1434 is positioned so as toreduce or eliminate any shadows on the patient's body during thesurgery.

The proximal overhead position of the light fixture 1434 provides anexcellent location for the antennas 1416 of an interrogation anddetection system. There are five loop antennas 1416 visible in thelightshade 1432 illustrated in FIG. 14A. However, there may be moreantennas 1416 on a far side of the lightshade 1432, not visible in FIG.14A. The number of antennas 1416 located on the lightshade 1432 may beany number suitable for the interrogation process.

The lightshade 1432 may be attached to the light fixture 1434 byextendable and retractable support arms 1436. As noted, FIG. 14Aillustrates the lightshade 1432 in a retracted or undeployed position orconfiguration, raised relative to the light fixture 1434. The supportarms 1436 may include hinges 1438 or other linkages. The hinges 1436 orother linkages enable the lightshade 1432 to be moved to an extended ordeployed position or configuration, lowered relative to the lightfixture 1434 and the patient support surface, for example, asillustrated in FIG. 14B. In one embodiment the antennas 1416 of thelightshade 1432 may be operable in the raised position. In oneembodiment the antennas 1416 may be attached to the light fixture 1434in a form other than that of a lightshade 1432.

FIG. 14C shows a lightshade 1432 is coupled to the light fixture 1434without the use of supporting arms 1436, according to yet anotherillustrated embodiment.

The lightshade 1432 may be a flexible sheet carrying a number ofantennas 1416. The flexible sheet is coupleable to the light fixture1434 by wrapping the flexible sheet around the light fixture 1434 andsecuring the flexible sheet thereto. The lightshade 1432 may be attachedto the light fixture 1434 by hooks, hook and loop fastener (Velcro®),clips, or any other suitable fasteners or adhesives. Two ends of thelightshade 1432 may be attached to each other to create an opening sizedto securely receive a portion of the light fixture 1434 therein. In thisconfiguration the lightshade 1432 remains on the light fixture by virtueof having a smaller diameter opening than a diameter of the portion ofthe light fixture. The lightshade 1432 may alternatively be an integralpart of the light.

In one embodiment, the antennas 1416 of the lightshade 1432 arecommunicatively coupled to an interrogation and detection systeminterface 36. The interrogation and detection system interface 36 may belocated at any suitable position in the room or in another room. Theantennas 1416 may be connected to the system interface 36 by a wiredconnection (e.g., wire bundle 1450) or a wireless connection. The wirebundle 1450 may run along a ceiling, wall and/or floor of the operatingroom to communicatively couple with a controller 18. In one embodimentthe light fixture 1434 is attached to a mobile support which can bemoved about the room or even from one room to another. In one embodimentthe system interface 36 is also attached to the light fixture 1434. Inone embodiment the controller 18 may be attached to the mobile supportof the light fixture 1434 with the antennas 16 directly connected to thecontroller by 1450.

The function and operation of the interrogation and detection system 14in embodiments in which the antennas 1416 are coupled to a light fixture1434 may be substantially the same as those embodiments in which theantennas 1416 are coupled to the patient support structure 26.

While FIGS. 14A, 14B, illustrate the antennas 1416 in a particularnon-overlapping configuration, the antennas 1416 may be carried by thelampshade 1432 in any suitable configuration. In contrast to thepreviously described embodiments in which the patient support structurecarried the structures, the lightshade 1432 are unlikely to interferewith radiological imaging. Hence, the antennas 1416 may overlap eachother, or may be in a non-overlapping configuration. The antennas 1416may be attached to one or both exterior surfaces of the lightshade 1432.Alternatively the antennas 1416 may be formed within the lightshade1432, for example, via lamination or weaving. The lightshade 1432 may bemade of any material suitable to not interfere with the function of theantennas 1416.

FIG. 15A shows a drape or curtain 1542 that carries a number of antennas1516 according to one illustrated embodiment.

The terms drape and curtain are used interchangeably herein and in theclaims. The drape or curtain 1542 may, for example, be used on, over, orin conjunction with a table, bed, frame or other structure during amedical procedure. The drape or curtain 1542 may be coupled to a track1540 which surrounds a patient support structure 26. The track 1540 istypically in close proximity to the patient support structure andaffords a suitable location for the antennas 1516 of the interrogationand detection system 14. In one embodiment, the track may be fastened toa ceiling of a room, for example an operating room, patient room orphysician's office or examination room. In such an embodiment, a wirebundle 1550 may also be attached to the ceiling as the wire bundle runsto the system interface 36 or controller 18 situated elsewhere in thesurgical environment. The system interface 36 and controller 18 may beattached to a wall of the environment or may be in any other suitablelocation within the environment in which medical procedures areperformed. In another embodiment, the track 1540 may be supported by afreestanding structure or structure fixed or coupled to a floor of theroom such as a frame.

The antennas 1516 may be carried on either exterior surface of the drapeor curtain 1542 or be situated (e.g., laminated) within the drape orcurtain 1542. While FIG. 15A shows the antennas 1516 on two opposingsides of the patient support structure 26, the antennas 1516 may bepositioned on a few or greater number sides of the patient supportstructure 26 while in use. The drape or curtain 1542 may be selectivelydeployed and retracted along the track 1540 during use. For example, thedrape or curtain 1542 may be retained in a retracted, undeployedposition or configuration during times or periods when scanning orinterrogation is not being performed. The drape or curtain 1542 may bemoved to an extended, deployed position or configuration in preparationfor scanning or interrogation, for example, just prior to completing themedical procedures (e.g., surgery) and, for example closing the patient.In other embodiments, the drape or curtain 1542 may be retained in theextended or deployed position or configuration throughout the surgicalprocedure. The antennas 1516 may be connected to system interface 36 bymeans of the wire bundle 1550 extending from the curtain 1540.

FIG. 15B shows a sheet 1544 carrying a number of antennas 1516 whichsheet 1544 may be quickly hung on a rack or frame 1540. The term sheetis used interchangeably herein and in the claims the terms drape orcurtain. The term rack is used herein and in the claims interchangeablywith the term frame. The sheet 1544 can be hung from the rack 1540 byconnectors 1546. More than one sheet 1544 may be hung from the rack 1540on one or more sides of the patient support structure 26. The antennas1516 may be attached on either exterior surface of the sheet 1544 or besituated (e.g., laminated or woven) within the sheet 1544. While thesheet 1544 is illustrated as having four antennas 1516, there may be asfew or as many antennas 1516 on the sheet as desired. Connectors 1546may include hooks, clamps, or any other fastener suitable to attach thesheet 1544 to the rack 1540. The antennas 1516 may be connected to thesystem interface 36 by means of a wire bundle 1550 extending from thesheet 1544.

FIG. 16 shows a controller 1618, according to one illustratedembodiment.

The controller 1618 may include a housing 1670. The housing 1670 maycontain a motherboard 1672 with a number of ports or connectors 1674a-1674 f (collectively 1674) to communicatively couple the motherboard1672 to respective ones of the antennas (e.g., antennas 16). Themotherboard 1672 may also include a number of slot connectors 1676a-1676 f (collectively 1676) to physically receive respective plug-inboards 1678 a-1678 f (collectively 1678) and communicatively couple theplug-in boards 1678 to the motherboard 1672. There may, for example beone plug-in board 1678 for each antenna, each of the antennas 16 andplug-in boards 1678 constituting a separate channel. The motherboard1672 may include additional slot connectors, allowing expansion or usewith different antenna configurations or different patient supportstructures (e.g., surgical tables, patient beds). The plug-in boards1678 may each carry one or more circuits (e.g., analog and/or digitalcircuit components) configured to transmit interrogation signals fromthe respective antenna and to monitor the antenna for responses to theinterrogation signals. For example, the plug-in boards 1678 mayimplement or carry the circuits disclosed in U.S. patent applicationSer. No. 11/759,141 filed Jun. 6, 2007, U.S. Provisional PatentApplication Ser. No. 61/056,787 filed May 28, 2008, and U.S. ProvisionalPatent Application Ser. No. 61/091,667 filed Aug. 25, 2008, with orwithout change, which patent applications are incorporated herein byreference in its entirety.

The motherboard 1672 may also include one or more ports 1679 to receivecontrol signals, for example from the interrogation and detection systeminterface 36, 1336 (FIG. 1, FIG. 13A). The motherboard 1672 may alsoinclude one or more synchronization circuits 1680 configured to controland synchronize the operation of the various plug-in boards 1678. Thesynchronization circuit 1680 may be configured to cause one of theplug-in boards 1678 to transmit an interrogation signal from a firstantenna, and cause one or more of the other plug-in boards to monitorfor a response by a transponder to the interrogation signal. Forinstance, the synchronization circuit 1680 may cause the plug-in boards1678 to have all of the antennas monitor for a response to theinterrogation signal. Alternatively, the synchronization circuit 1680may cause the plug-in boards 1678 to have all of the antennas other thanthe antenna that transmitted a most recent interrogation signal monitorfor a response. Such may advantageously allow monitoring sooner thanwould otherwise be possible since such can avoid the need to allow thetransmitting antenna to return to a quiescent state after transmittingbefore monitoring for a response. The synchronization circuit 1680 maysynchronize the plug-in boards 1678 to successively cause the variousantennas to transmit, for example starting with an antenna at one end,and successively transmitting from each of the antennas in order alongthe longitudinal axis 30 (FIGS. 1 and 2). Alternatively, thesynchronization circuit may synchronize the plug-in boards 1678 to causethe various antennas to transmit, but not in order along thelongitudinal axis 30. As a further alternative, the synchronizationcircuit 1680 may synchronize the plug-in boards 1678 to cause thetransmission of interrogations signals from a subset of the total set ofantennas.

While illustrated as a motherboard 1672 and plug-in boards 1678, otherembodiments are possible. For example, the various antennas may becontrolled by respective circuits integrated into a signal circuitboard. Alternatively, the various antennas may be controlled by a singlecircuit.

FIG. 17 shows a control system 1700 of a controller of an interrogationand detection system, according to one illustrated embodiment.

The control system 1700 includes a field programmable gate array (FPGA)board 1702, one or more analog boards 1704, and a display board 1706,communicatively coupled to one another. The analog board(s) 1704 maytake the form of one or more plug-in boards 1678, as discussed inreference to FIG. 16. Hence, there may be a respective analog board 1704for each of the antennas 16 (FIGS. 1 and 2).

The FPGA board includes an FPGA 1708, configuration jumpers 1710, RS-232drivers 1712, oscillator 1714, random access memory (RAM) 1716, flashmemory 1718, and voltage monitoring (VMON) analog-to-digital converter(ADC) 1720.

The FPGA 108 may take the form of a Xilinx Spartan 3 FPGA, which runsFPGA and application software. As explained below, on power up, the FPGAreads the configuration information and application software programfrom the flash memory 1718.

The configuration jumpers 1710 are used to select the applicationsoftware configuration.

The RS-232 drivers 1712 are used to allow the application software tocommunicate using serial RS-232 data for factory test and diagnostics.

The oscillator 1714 sets the clock frequency for the operation of theFPGA 1708. The oscillator 1714 may, for example, take the form of 40 MHzoscillator, although other frequencies are possible.

The RAM 1716 is connected to the FPGA 1708 and is available for use bythe application software. The application software uses this memoryspace for storage of both the executable program and program data. TheRAM 1716 may, for example, have a capacity of 1 MB.

The flash memory 1718 contains both the FPGA configuration data and thebinary application program. On power up the FPGA 1708 reads the flashmemory to configure the FPGA 1708 and to copy the application programbinary data from the flash memory 1718 to the RAM 1702.

The voltage monitor ADC 1720 is connected to the FPGA 1708 andcontrolled by the application software to monitor a power supply andregulated voltage forms in controller electronics.

The analog board 1704 includes transmit control circuits 1722, capacitorselection circuits 1724, an antenna detection circuit 1726, signal ADC1728, audible beeper 1730 and self-test signal 1732.

The transmit control circuits 1722 on the analog board 1704 arecontrolled by signals from the FPGA 1708 to generate a transmitwaveform. These signals are denominated as LO_FET_ON and HI_FET_ON,which control the transmit or drive transistors Q1, Q2 (FIG. 18A) alongwith a signal denominated as DUMP_ON which controls a dump TRIAC (FIG.18A).

Optional capacitor selection circuits 1724 on the analog board 1704 arecontrolled by the signals from the FPGA 1708 to tune the drive circuitto match an inductance of the antenna 16 (FIGS. 1 and 2).

The antenna detection circuit 1726 detects when an antenna 16 (FIGS. 1and 2) is connected to the controller 20. The output of the antennadetection circuit 1726 drives a signal denominated as the LOOP_LEVEL_OUTsignal, which is an input to the FPGA 1708.

The signal ADC 1728 is used to sample the signals received at theantenna 16 from the transponders 24 (FIG. 1). The signal ADC 1728 may,for example, operate at a 1 MHz sample rate and may have 12-bits ofresolution. The FPGA board 1702 generates the timing and control signalsfor the signal ADC 1728, which signal are denominated as ADC_CTRL, CS1,SCLK, SD0.

The aural indicator (e.g., speaker or beeper) 42 (FIGS. 1 and 2) can becontrolled by the FPGA 1708 to emit sounds to indicate various states,modes or operating conditions to the medical provider.

The FPGA 1708 can cause the generation of the self test signal 1732 onthe analog board 1704 at the signal ADC 1728. Self-testing may beperformed at start up, and/or at other times, for example periodicallyor in response to the occurrence of certain conditions or exceptions.

The display board 1706 includes user interface elements, for example anumber of visual indicators (e.g., LEDs, LCDs, etc.) 40 (FIGS. 1 and 2).The FPGA board 1702 can control the visual indicators 40 on the displayboard 1706. The display board 1706 also includes a user selectableactivation switch 44, denominated as front panel button 1736. The frontpanel button 1736 is connected to the display board 1706 which allow theFPGA 1708 to monitor when the front panel button 1736 is activated(e.g., pressed).

FIG. 18 shows a software configuration 1800 of the interrogation anddetection system 14, according to one illustrated embodiment.

The software may include application software 1802 that is responsiblefor operating the controller 18 (FIGS. 1 and 2). The applicationsoftware 1802 controls the timing for generating transmit pulses,processes sampled data to detect transponders 24 (FIGS. 1 and 2), andindicates status to the user with the visual indicators 40 (FIGS. 1 and2) on the display board 1706 (FIG. 17) and/or via the aural indicator 42on the analog board 1704 (FIG. 17). The application software 1802 isstored in the flash memory 1718 (FIG. 17) and transferred into the RAM1716 by a boot loader 1804.

The boot loader 1904 is automatically loaded when the FPGA 1708 isconfigured, and starts execution after a processor core 1806 is reset.The boot loader 1804 is responsible for transferring the applicationsoftware 1802 from the flash memory 1718 to the external RAM 1716.

The processor platform 1808 is configured into the FPGA 1708 (FIG. 17)on power up from the configuration information stored in the flashmemory 1718. The processor platform 1808 implements a custommicroprocessor with a processor core 1806, peripherals 1810 a-1810 n,and custom logic 1812.

The processor core 1806 may take the form of a soft processor coresupplied by XILINX under the name MICROBLAZE™, that implements a 32-bitprocessor including memory cashes and a floating point unit. A soft coreprocessor is one that is implemented by interconnected FPGA logic cellsinstead of by a traditional processor logic. The processor core 1806 isconnected to the internal FPGA peripherals 1810 a-1810 n using a 32-bitprocessor bus 1811 called the On-Chip Peripheral Bus. The XILINXsupplied peripherals for the MICROBLAZE™ processor core 1806 includeexternal memory interfaces, timers, and general purpose I/O.

The custom logic 1812 to create the transmit signals, sample the ADC,and accumulate the transponder return signals is designed as aperipheral to the processor core 1806. The custom logic 1812 is the partof the design of the FPGA 1708.

Some embodiments may substitute a full microprocessor for the softprocessor core. Thus, for example, a microprocessor such as the ATOM™processor, commercially available from Intel Corporation, may beemployed in place of the MICROBLAZE™ processor core. The fullmicroprocessor may be communicatively coupled to multiple analog antennachannels via one or more FPGAs and one or more suitable buses. The FPGAmay, for example, act as a co-processor and/or cache. Additionally, oralternatively, a higher bandwidth bus architecture may be employed. Forexample, a PCI Express™ or PCIe™ bus architecture may be employed,rather than an ISA bus architecture. Suitable FPGAs may include thosefrom ATMEL Corporation. Such FPGAs may advantageously have built in PCIebus architecture, allowing easy integration. This approach may enablemore I/O ports, such as USB ports, may provide more or better videooptions, and may provide faster data rates from the analog antennachannels that otherwise possible using the ISA bus architecture and softprocessor core approach.

FIGS. 19A-19I show a control circuit 1900 according to one illustratedembodiment. The control circuit 1900 is used to drive the antenna 16(FIGS. 1 and 2) to excite or interrogate transponders 24 (FIGS. 1 and2), and to detect and process signals received by the antenna 16 fromthe transponders 24. As previously noted, there may be a respectivecontrol circuit 1900 for each of the antennas 16, or a single controlcircuit may be configured to control multiple antennas.

The control circuit 1900 includes a transmitter circuit 1902 formed by apair of drive transistors (e.g., field effect transistors) Q1, Q2operated in a push-pull configuration between a high voltage rail (e.g.,24 V) and a low voltage rail (e.g., GND). The drive transistors Q1, Q2are responsive to respective drive signals DRIVE_HI, DRIVE_LO, which areapplied to the gates of the respective drive transistors Q1, Q2. Thedrive transistors Q1, Q2 are coupled to the antenna 16 by a non-switchedcapacitor C8 and the coaxial cable 20. The antenna 16 and capacitor C8,as well as capacitance provided by the coaxial cable 20, form an LCcircuit.

Optionally, the control circuit 1900 may also include a dynamic tuningcircuit 1904. The dynamic tuning circuit 1904 selectively adjusts thecapacitance of the LC circuit. In the illustrated embodiment, thedynamic tuning circuit 1904 includes a number of switched capacitorsC33-C36 and relays U9, U10. The relays U9, U10 are operated toselectively couple the switched capacitors C33-C36 in series with thenon-switched capacitor C8, thereby adjusting the LC characteristics ofthe LC circuit, and allowing fine tuning of the LC circuit around centerfrequencies or center channels of a number of wide band frequency bands,as described in more detail below.

FIG. 20 illustrates a detection cycle 2000 that employs an approach thatoptimizes signal to noise ratio (SNR), according to one illustratedembodiment. Such may, for example, advantageously increase range orincrease sensitivity at a given range.

One embodiment is optimized based on having an overall detection cyclethat performs well for transponders with resonant frequencies fromapproximately 136 KHz to approximately 154 KHz, and which has a pulsetiming that is consistent with hardware limitations. An optimal SNR maybe achieved by, for example, transmitting a single wideband frequencypulse.

The application software 1802 (FIG. 18) implements the detection cycle2000 using transmission or interrogation in a frequency band centeredaround a center channel or frequency. In the illustrated embodiment, theapplication software 1802 sequences through a non-measurement portion(i.e., gap) 2000 a, and two distinct measurement portions, denominatedas a noise detection portion 2000 b and an interrogation or signaldetection portion 2000 c, each detection cycle 2000. In at least oneembodiment, the detection cycle 2000 may, for example, be approximately275 milliseconds, the gap portion may be approximately 10 milliseconds,the noise portion approximately 37 milliseconds and the interrogation orsignal portion approximately 228 milliseconds.

During the noise detection portion 2000 b, which may, for example be afirst measurement portion of each detection cycle 2000, ambient orbackground noise is measured or sampled, providing a value indicative ofa level of ambient or background noise for the particular environment.The noise measurements or samples are taken or captured at a timesufficiently after excitement of the transponders 24 (FIG. 1) by theinterrogation signal emitted by the transmitter such that thetransponders 24 are substantially not resonating or responding to anyprevious excitation by interrogation signals. In particular, a number Nof measurements or samples are taken during the noise detection or firstmeasurement portion 2000 b.

During the interrogation portion 2000 c, which may, for example take theform of the second measurement portion of each detection cycle 2000,responses by transponders 24 are measured or sampled. The responsemeasurements or samples are taken with the transmitter transmitting orat a time sufficiently close to excitement of the transponders 24 by theinterrogation signal emitted by the transmitter such that thetransponders 24 are still substantially resonating or responding to theinterrogation signal. In particular, a number M of measurements orsamples are taken during the interrogation or second measurement portion2000 c.

While the interrogation portion 2000 c is illustrated as one contiguousor continuous portion 2000 c, in some embodiments the interrogationportion 2000 c may take the form of two or more separate portions orintervals. Each of the portions 2000 c may employ the same transmitfrequency band, for example centered around 145 KHz. Other centerchannels or frequencies may for example be 136 KHz, 139 KHz, 142 KHz,145 KHz, 148 KHz, 151 KHZ and/or 154 KHz, or any other frequencysuitable for exciting the transponder to resonate. Some embodiments mayemploy frequency hopping, for example transmitting a different centerchannel or frequency for each of a plurality of interrogation portions2000 c of each detection cycle 2000. Such is discussed further in U.S.provisional patent application Ser. No. 60/892,208, filed Feb. 28, 2007and U.S. non-provisional application Ser. No. 11/743,104, filed May 1,2007.

The gap portion 2000 a may provide time for the response of thetransponders 24 to the interrogation signal to decay sufficiently toallow measurement of noise.

Some embodiments may arrange the gap 2000 a, the noise detection portion2000 b and/or the interrogation portion 2000 c, or parts thereof, in adifferent order.

In one embodiment, the time to accumulate the noise sample or valueindicative of a noise level may, for example, be approximately 37milliseconds, and the time to accumulate the transponder signalmeasurement approximately 228 milliseconds. Along with a gap 2000 a ofapproximately 10 milliseconds between the signal and noise portions, thetime for a single detection cycle 2000 would be approximately 275milliseconds. As noted above, the transmitter is OFF during the noisemeasurement portion 2010 b of each detection cycle to measure ambientnoise, and the signal measurement portion 2010 c is taken with thetransmitter transmitting a wideband interrogation signal about theparticular center channel or frequency.

The noise samples may be accumulated and a highest one or more ofmultiple samples or measurements over one or more detection cyclesselected or used to prevent unwarranted fluctuations. The responsesignals from the transponder 26 may be accumulated and/or averaged orintegrated over one detection cycle or over multiple detection cycles.

The number N of noise measurements or samples and/or the number M ofresponse measurements or samples may be selected to achieve a desiredratio of N to M, in order to achieve or maintain a desired signal tonoise ratio. For example, obtaining 200 noise measurements or samplesand 800 response measurements or samples each detection cycle results inan SNR of approximately 2 (e.g., the square root of the 800 divided by200). While an SNR as low as 1.1:1 may be sufficient in someembodiments, an SNR approaching 2:1 ensures sufficient differentiationto eliminate or reduce the possibility of false positives to anacceptable level for the particular applications envisioned herein. Anyknown hardware and software accumulators, summer, integrators and/orother hardware or software may be suitable.

FIG. 21A illustrates pulse timing, according to one illustratedembodiment.

The custom logic in the FPGA 1708 (FIG. 17) generates the timing andcontrol signals for each pulse 2110. During a transmit portion 2110 a ofthe pulse 2110, the logic of the FPGA 1708 drives the drive transistorcontrol lines to generate the transmit signal. The FPGA logic controlsthe frequency of the transmit signal. During a dump portion 2110 b ofthe pulse 2110, the logic of the FPGA 1708 drives the gate of the dumpTRIAC T1 to quickly drain the transmit energy from the antenna 21 inorder to allow detection of the response signal form the transponder 24,if any. A recovery portion 2110 c of the pulse 2110 allows receiverfilters and amplifiers to recover from the transmitted pulse beforedetecting the response signal from the transponder 24, if any. Duringthe receive response portion 2110 d of the pulse 2110, the FPGA 1708controls the signal ADC 1728 to sample the response signal from thetransponder 24, if any. The signal ADC 1728 may, for example, sample ata 1 MHz sample rate with a 12-bit resolution. A dither portion 2110 e ofthe pulse 2110 has a random variable length of time, and may, forexample be generated by a pseudo-noise (PN) sequence generator. Adding arandom length of time between pulses de-correlates the response signalreceived from the transponder 24 from constant frequency sources ofinterference, if any.

For example, within each of 228 millisecond signal measurement intervals400 c discussed above, the custom logic of the FPGA 1708 (FIG. 17)accumulates the received signals from, for example 800 pulses.

FIG. 21B illustrates pulse timing, according to one illustratedembodiment. The pulse timing is similar in some respects to thatillustrated in FIG. 21A, hence similar or identical structures, acts orfeatures are identified using the same reference numbers. Onlysignificant differences between the two are discussed below.

In contrast to the embodiment of FIG. 21A, the embodiment of FIG. 21Bmay advantageously eliminate the dump portion 2110 b of the pulse 2110.Such may be omitted, for example, where the antenna 21 that transmittedthe most recent interrogation signal is not being used to monitor for aresponse to the interrogation signal. Such may advantageously allowmonitoring for the response to occur sooner than would otherwise bepossible if the dump portion 2110 b were needed.

Also in contrast to the embodiment of FIG. 21A, the embodiment of FIG.21B may advantageously eliminate the recovery portion 2110 c of thepulse 2110. Such may be omitted, for example, where the antenna 16 thattransmitted the most recent interrogation signal is not being used tomonitor for a response to the interrogation signal. Such mayadvantageously allow monitoring for the response to occur sooner thanwould otherwise be possible if the recovery portion 2110 c were needed.

Removal of the dump portion 2110 b and/or recovery portion 2110 c mayallow for a more favorable sampling rate or better resolution or mayallow a longer noise detection portion, which may significantly enhanceperformance.

FIG. 22 shows signal timing for driving the drive transistors Q1, Q2(FIG. 19A), according to one illustrated embodiment.

The custom logic in the FPGA 1708 (FIG. 17) generates the signals 2220a, 2220 b to drive the drive transistors Q1, Q2 (FIG. 19A) during thetransmit portion 2110 a (FIG. 21) of the pulse 2110. A transmit (TX)period value is used by the logic of the FPGA 1708 to set the transmitfrequency. The low transistor (e.g., Low FET) Q2 turns ON at thebeginning of the transmit period. The Low FET off value controls whenthe low transistor (e.g., Low FET) Q2 is turned OFF. The low transistorQ2 is turned OFF before the high transistor (e.g., High FET) Q1 isturned ON to avoid a short circuit through the transistors Q1, Q2. TheHigh FET on value controls when the high transistor (e.g., High FET) Q1is turned ON. The High FET Off value controls when the high transistorQ1 is turned OFF. The high transistor is turned OFF before the lowtransistor Q2 is turned ON to avoid a short circuit through thetransistors Q1, Q2. For example, to achieve a transmit frequency of144.9 KHz, the transmit period should be set to 6.9 μsec. Also forexample, a suitable duration that both the low and high transistors Q1,Q2 are OFF may be set to 400 nsec.

The ADC converts the signal received from the transponder 24, if any,from analog to digital. Such conversion may, for example, be performedat a sampling rate of 1 MHz with a 12-bit data resolution. The sampledADC data is then accumulated together or integrated, for example over800 measurements or samples, to compute the total summed response signalreceived from the transponder 24, if any.

The accumulated or integrated received signal may be match filtered withboth in-phase and quadrature reference signals to determine the signalmagnitude. The received receive signal is matched filtered with aplurality of reference signals, for example with the seven referencesignals, for instance as shown in Table 1 below. Some embodiments, mayemploy match filtering before accumulating or integrating the receivedsignal.

TABLE 1 Match Frequency 136 KHz 139 KHz 142 KHz 145 KHz 148 KHz 151 KHz154 KHz

The maximum value for the matched filters (e.g., seven matched filters)with active transmit is compared with an adjusted detection threshold.If the maximum value is greater than the detection threshold, then aresponse signal from a transponder 26 is considered as having beendetected, and appropriate action is taken.

Noise faults may be detected as well as antenna transmit voltage faults.Noise faults may be detected when the matched filter output during thenoise detection portion is greater than a noise fault threshold (e.g., athreshold magnitude 2.7 mV over a threshold time, e.g., 7 seconds orthreshold magnitude 7 mV over a time threshold of 7 seconds). Antennatransmit voltage faults may be detected when the antenna transmitvoltage drops below an antenna voltage fault threshold (e.g., 270V_(Peak-to-Peak)). Two environmental faults in a row such as the above,may trigger an Environmental Error Mode, while two normal measurementsin a row may return to a normal Scan Mode. Faults in general arediscussed in more detail below. Alternatively, the interrogation anddetection system may employ a fast Fourier transform approach in lieu ofmatch filtering.

FIG. 23A shows a method 2300 of operating the interrogation anddetection system 14, according to one illustrated embodiment.

The method 2300 starts at 2302. For example, the method 2300 may starton application of power to the interrogation and detection system 12 orin response to activation of a switch by a user such as a clinician,surgeon

In response to detecting an application of power, the interrogation anddetection system 14 may enter a Power-Up mode. The Power UP mode 502may, for example, in response to the application of power to thecontroller 18 and turning ON the switch on the controller 18. In thePower-Up mode, a Power indicator (e.g., LED) may be turned ON orilluminated, and may remain ON or illuminated as long as the power isapplied and the switch is in the ON state. In response to entering thePower UP mode, the software 1800 may perform software initialization,built in tests, and an audio/visual test. If a fault is detected, thesoftware 1800 may progress to a System Fault Mode. If no faults aredetected, the software 1800 may turn a System Ready indicator (e.g., LEDgreen), and enter an antenna Detection Mode. In the System Fault mode,the software 1800 may cause an indication of the detection of a systemfault by blinking a System Ready indicator (e.g., LED) yellow, and/orissuing a sequence of rapid beeps or other sounds. The corrective actionfor the System Fault Mode may be to cycle power to reinitiate the PowerUp mode. Continued failure indicates a failed controller 18.

In the Antenna Detection Mode, the software 1800 checks for antennas 16connected to the controller 18. The Antenna Detection Mode may beindicated by turning the System Ready indicator (e.g., LED) green andturning the Antenna Ready indicator (e.g., LED) OFF. If no antenna 16 isdetected, the software 1800 remains in the Antenna Detection Mode. Ifone or more antennas 16 are detected, the software 1800 makes note ofthe total number of antennas and progresses to the AntennaInitialization Mode.

At the start of the Antenna Initialization Mode, after the detection ofthe antennas 16, the software 1800 may turn the Antenna Ready indicator(e.g., LED) yellow and optionally check for the presence of a respectivefuse coupled to antennas 16. If a fuse is found, the software 1800 mayattempt to blow the fuse and verify that the fuse was correctly blown.After the fuse is blown the software 1800 may verify that respectiveantenna 16 is operating within tolerances. The software 1800 mayindicate that the antenna 16 is ready by turning the Antenna Readyindicator green. The software 1800 may also start a timer which willallow the antenna 16 to be disconnected and reconnected to thecontroller for a period to time (e.g., 5 hours) after the fuse is blown.The controller 18 may determine the adjustments or fine tuning to bemade about the center frequencies or channels during AntennaInitialization Mode. In particular, the controller 18 may determine theparticular frequency in each of the frequency bands that elicits theresponse with the highest voltage. The controller 18 may determine suchbe varying the capacitance of the LC circuit using the switchedcapacitors C33-C36 during the Antenna Initialization Mode. Theparticular combination of switched capacitors C33-C36 which achieved theresponse with the highest voltage may then be automatically employedduring the Scan Mode (discussed below) to adjust or fine tune about thecenter frequency or channel in each broad band of transmission. Otherapproaches to determining the fine tuning may be employed.

If the software 1800 does not successfully complete the AntennaInitialization Mode, the software 1800 enters an Invalid Antenna Mode.If the software 1800 successfully completes the Antenna InitializationMode, the software 1800 progresses to the Scan Mode to automaticallystart scanning. In the Invalid Antenna Mode, the software 1800 may blinkthe Antenna Ready indicator yellow and issues a slow beep pattern. TheInvalid Antenna Mode may be entered in response to any of the followingconditions: 1) the antenna 16 connected to the controller 18 is out oftolerance; 2) the controller 18 is unable to blow the fuse of theantenna 16; 3) the antenna 16 does not have a fuse and more than the settime period has past (e.g., 5 hours) since a fuse was blown; 4) theantenna 16 does not have a fuse and the controller 18 has beenrestarted; 5) the antenna 16 has been connected to the controller 18 formore than the set time period (e.g., 5 hours); 6) the antenna 16 isdetuned due to close proximity to metal. The corrective action for theInvalid Antenna Mode is to remove the invalid antenna 16 and attach anew antenna 16 to the controller 18 that contains a fuse or to reconnectthe antenna 16 while holding it in the air at least 2 feet away fromlarge metallic objects. The software 1800 enters the Scan Mode when theantennas 16 are ready and the operator presses a Start/Stop button. Thesoftware 1800 may issue a short three beep pattern via the speaker orbeeper when entering the Scan Mode to identify the entry to the user.

In the Scan Mode, the software 1800 may continuously or periodicallyperform the following functions: 1) look for response signals fromtransponders 24; 2) monitor the noise level; 3) insure the antennas 16are connected and operating correctly; and 4) blink the appropriateindicator in a circular pattern. The interrogation and monitoring forresponse may be performed using a detection cycle, such as that set outin FIGS. 21A, 21B and the description related to those Figures. While,not specifically set out in FIG. 18, such may also include optimizationof signal to noise ratio, such as set out in FIG. 20 and the descriptionrelated thereto.

At 2304, a timer starts. The timer allows a limit to be set on theamount of time spent scanning for a transponder 24 (i.e., scan maximumtime interval). Alternatively, a counter could be employed to set alimit of the number of iterations that the antennas 16 are successivelyemployed to transmit interrogation signals.

At 2306, an antenna counter i is set, for example set to 1. The antennacounter allows the method 2300 to successively iterate through each of anumber N of antennas 16 to transmit the interrogation signal. The numberN of antennas 16 may have been determined during the Antenna DetectionMode.

At 2308, an interrogation signal is transmitted from an i^(th) antenna16. In particular, the FPGA 1708 (FIG. 17) may cause one of the plug-inboards to cause the antenna 16 coupled thereto to transmit aninterrogation signal. The interrogation signal may advantageously takethe form of an unmodulated interrogation signal, for example in theradio or microwave portions of the electromagnetic spectrum.

At 2310, one or more antennas 16 are monitored for a response to theinterrogation signal. In particular, a number of the plug-in boards maymonitor the respective antenna coupled thereto for the response to theinterrogation signal. For example, all of the antennas 16 may bemonitored to a response to the interrogation signal. Alternatively, allexcept the antenna 16 that transmitted the most recent interrogationsignal (i.e., i^(th) antenna) may be monitored for a response to theinterrogation signal. As another alternative, some subset of all of theantennas 16 may be monitored for a response to the interrogation signal.The response may advantageously take the form of an unmodulated responsesignal, for example in the radio or microwave portions of theelectromagnetic spectrum.

At 2312, it is determined if a response to the interrogation signal wasreceived. For example, the FPGA 1708 (FIG. 17) may poll or otherwisemonitor each of a number of plug-in or analog boards to determine if aresponse signal was detected via any of the antennas coupled to thoseplug-in or analog boards. If a response to the interrogation signal wasreceived, a suitable indication is provided at 2314, and the method 2300terminates at 2316. For example, when an appropriate response signalfrom a transponder 24 is detected while in Scan Mode, the software 1800may turn ON an amber DETECT indicator (e.g., LEDs) and/or provide anaudible alarm. The alarm may, for example, beep a continuous solid toneas long as the transponder is detected, with a minimum of beep durationof, for instance 0.5 second. If a response to the interrogation signalwas not received, it is determined whether there are additional antennasto transmit the interrogation signal from at 2318.

If there are additional antennas to transmit from, the counter isincremented at 2320 and control returns to 2308 to transmit via the nexti+1^(th) antenna 16. This can allow iteration through a number ofantennas 16 as the antenna that transmits the interrogation signal. Aspreviously explained, antennas 16 may be operated to transmit aninterrogation signal in an order of appearance along a longitudinal axisof the patient support surface or may be operated in any other order.Also as previously noted, all or some lesser number of antennas may beemployed to transmit the interrogation signal in any single pass oriteration through the set or subset of antennas 16.

If there are not further antennas to transmit the interrogation signalfrom, it is determined if a time limit (i.e., scan maximum timeinterval) has been exceeded at 2322. If the time limit has been exceededthe method 2300 terminates at 2316. If the time limit has not beenexceeded, the counter is reset at 2306. This allows multiple passesthrough the use of each antenna in a set or subset of antennas 16 as theinterrogating antenna 16. When the operator or user pushes theStart/Stop button or the a scan maximum time interval (e.g., 4 minute)has been reached, the software 1800 may issue a short three beep patternand return to the Antenna Ready Mode.

If the software 1800 detects that one of the antennas 16 is disconnectedwhile in the Scan Mode, the software 1800 enters the Scan Fault Mode. Inthe Scan Fault Mode, the software 1800 may issue a sequence of rapidbeeps and blink ON and OFF the amber DETECT indicator. The Scan FaultMode can be cleared by pushing the Start/Stop button. The software 1800will automatically clear the scan fault mode after 10 beeps.

While in the Scan Mode, if excess noise or loss of transmit signal isdetected, the software 1800 may progress to the Environment Error Mode.In the Environment Error Mode, the software 1800 may issue or produce anappropriate indication. For example, the software 1800 may cause theproduction of a sequence of slow beeps and the blinking ON and OFF thegreen circle indicator. The corrective action for the Environment ErrorMode is to reposition the antenna with respect to any large metalobjects or sources of electrical interference. The software 1800 mayautomatically stop the scan if the environment error condition lasts formore than a set time or number of beeps (e.g., 5 beeps).

FIG. 23B shows a method 2310 b of monitoring all antennas for a responseto an interrogation signal, according to one illustrated embodiment.

At 2318, an interrogation and detection system monitors all antennas 16for a response to the interrogation signal.

FIG. 23C shows a method 2310 c of monitoring all antennas except atransmitting antenna for a response to an interrogation signal,according to one illustrated embodiment.

At 2320, an interrogation and detection system monitors all antennas 16for a response to the interrogation signal, except the antenna 16 thetransmitted the most recent interrogation signal.

FIG. 24A shows a method of operating an interrogation and detectionsystem to detect transponders 2400 a, according to one illustratedembodiment.

The method 2400 a starts at 2401. For example, the method 2400 a maystart when the interrogation of detection system is turned ON, or whenpower is supplied, or in response to a call from a procedure orfunction.

At 2402, an antenna counter I is set, allowing the method 2400 a toiterate through one or more antennas (n) of the interrogation anddetection system. The interrogation and detection system iteratesthrough the antennas by transmitting interrogations signals successivelyfrom each of a number of the antennas, typically one antenna at a time,and monitoring or listening for response signals on one or more of theantennas.

At 2403, the interrogation and detection system measures averaged noiseand averaged signals. At 2404, the interrogation and detection systemprocesses the averaged noise and averaged signal, and at 2405 determineswhether a transponder (i.e., return or response signal from transponder)has been detected.

In the embodiment illustrated in FIG. 24A, the interrogation anddetection system requires more than one (e.g., two) successivedetections of the transponder to conclude that the signal detectedindicates the presence of a transponder. Such prevents against falsepositive determinations. Hence, at 2406, the interrogation and detectionsystem again measures averaged noise and averaged signals. At 2407, theinterrogation and detection system again processes the averaged noiseand averaged signal and at 2408 determines whether a transponder (i.e.,return or response signal from transponder) has been detected.

If a transponder has been detected an adequate number of times (e.g.,twice), the interrogation and detection system provides notification at2409. Notification may, for example, include sending an electrical oroptical signal and/or producing a visual, aural or tactile alert to auser (e.g., medical service provider). If the interrogation anddetection system determines that a transponder has not be detected ateither 2405, 2407, control passes to 2410.

At 2410, the interrogation and detection system determines whether thereare further antennas to iterate through. If so, the antenna counter isiterated, and control returns to 2403. If not, the method 2400 a, mayterminate at 2412. Alternatively, the method 2400 a may return to 2402and continuously repeat as long as power is supplied to theinterrogation and detection system.

FIG. 24B shows a method of operating an interrogation and detectionsystem to sample noise and responses and to adjust sampling times andperform noise correction 2400 b, according to one illustratedembodiment, the method useful with the method of FIG. 24A.

The method 2400 b starts at 2420. For example, the method 2400 b maystart in response to a call from a procedure that implements the method2400 a. The method 2400 b may, for example, be employed in measuringaveraged noise and averaged signal 2403 (FIG. 24A).

At 2421 a transmitter of the interrogation and detection system is OFF(i.e., not transmitting interrogation signals) or is turned OFF if notalready OFF. This starts a noise detection portion of a transponderdetection cycle. At 2422 ambient noise received by the antennas issampled. For example, ambient noise detected by all of the antennas maybe sampled by the interrogation and detection system.

At 2423, the interrogation and detection system determines noisecancellation factors for each antenna. The interrogation and detectionsystem may employ a variety of approaches for determining the noisecancellation factors, for example computing a noise cancellation factorfor each antenna based on ambient noise detected on all of the otherantennas except the antenna for which the respective noise cancellationfactor is being computed.

At 2424, the interrogation and detection system determines a sampleaveraging time for sampling nose based on the measured ambient noiselevel. At 2425, the interrogation and detection system determines asample response averaging time based on the measured ambient noiselevel. The sample averaging times determine how long samples of noise orresponse will be averaged in determining noise or response measurementsor levels. Such dynamic determination of sample averaging times allowsthe interrogation and detection system to accommodate a changing noiseenvironment. For example when a piece of equipment is introduced orremoved from the environment or a piece of equipment turns ON or OFF, orotherwise changes amount or frequency distribution of noise it generatesin the environment. Thus, the interrogation and detection system mayobtain adjust the noise floor to increase range in real time or almostreal time in response to the actual noise in the environment.

At 2426, the interrogation and detection system averages noise correctednoise samples for the noise sample averaging time. As noted above, thenoise sample averaging time may be determined dynamically. The noisesamples may be corrected, for example, using the determined nosecancellation factors.

At 2427, the interrogation and detection system transmits interrogationsignal(s) from one of the antennas. As previously noted, theinterrogation and detection system my iterate through the antennas oneat a time, for example using an antenna counter I. At 2428, theinterrogation and detection system averages noise corrected responsesfor the response averaging time. As noted above, the response sampleaveraging time may be determined dynamically. The response samples maybe corrected, for example, using the determined nose cancellationfactors. It is noted that as received, the response signals typicallycontain a mix of signal and noise, hence is generally referred to hereinas responses. After noise correction, the result is theoretically puresignal. In practice there may be some still be some amount of noiseremaining, however the signal will typically dominate the noise afternoise correction.

The method 2400 b may terminate at 2429, for example until called againby the procedure that implements 2400 a (FIG. 24A) to transmitinterrogation signals from a next antenna.

FIG. 24C shows a method of operating an interrogation and detectionsystem to determine whether a transponder has been detected 2400 c,according to one illustrated embodiment, the method useful with themethod of FIG. 24A.

The method 2400 c starts at 2440. For example the method 2400 c maystart in response to a call from a procedure that implement the method2400 a (FIG. 24A). The method 2400 c may, for example, be employed inprocessing transponder detection 2404 (FIG. 24A).

FIGS. 25A-25E are flow diagrams of methods of operating an interrogationand detection system by measuring and/or compensating for noise,according to various illustrated embodiments, the methods useful withthe method of FIG. 24A.

At 2441, the interrogation and detection system transforms the averagednoise and response samples from a time domain to a frequency domain. Theinterrogation and detection system may, for example, perform fastFourier transforms on the averaged samples. At 2442, the interrogationand detection system may find a peak of response fast Fouriertransformed spectrum data.

At 2443, the interrogation and detection system determines an amplitudethreshold based on the averaged noise level. At 2444, the interrogationand detection system determines whether the response amplitude is equalor exceeds the determined amplitude threshold. If so, control passes to2445. If not, control passes to 2448 where a signal may optionally beproduced indicative of no tag being detected.

At 2445, the interrogation and detection system determines whether thesignal is in appropriate frequency range. While the frequency range isillustrated as being between 137 KHz and 165 KHz, inclusive, otherfrequency ranges may be employed depending on the specific structure andfrequency of the transponders. The disclosed embodiments are particularsuited for use with low Q transponders in which the response frequenciesof various transponders are not closely controlled, advantageouslyallowing large manufacturing tolerances to reduce cost. If the signal isin the appropriate frequency range, control passes to 2446, otherwisecontrol goes to 2448.

At 2446, the interrogation and detection system determines the Q valueof the response. For example, the interrogation and detection system maycompute the slope of the received signal decay at a number of windows(e.g., 5 windows). At 2450, the interrogation and detection systemdetermines if the determined Q value is greater than or equal to athreshold Q value (e.g., 35). While the threshold Q value is illustratedas being 35, other Q values may be employed depending on the Q value(s)of the specific transponders. If the tag response Q value below the Qvalue threshold, the interrogation and detection system determines thata transponder has been detected at 2450. If the tag response Q value isequal or above the Q value threshold, the interrogation and detectionsystem determines that a tag has not been detected 2448.

The method 2400 c may terminate at 2449, for example until called againby the procedure that implements the method 2400 a (FIG. 24A).

FIG. 25A shows a method 2500 a of measuring or sampling responses,according to one illustrated embodiment.

In particular, at 2510, the interrogation and detection system measuresor samples response on all antennas or antenna channels.

FIG. 25B shows a method 2500 b of determining noise estimates, accordingto one illustrated embodiment.

In particular, at 2520, the interrogation and detection systemdetermines noise estimates based on measures or samples from allantennas or antenna channels other than the respective antenna orantenna channel for which the noise estimate will provide thecompensation factors.

FIG. 25C shows a method 2500 c of determining noise estimates, accordingto one illustrated embodiment.

In particular, at 2530, the interrogation and detection systemdetermines an average noise estimate based on averaging of measures orsamples from all antennas or antenna channels other than the respectiveantenna or antenna channel for which the noise estimate will provide thecompensation factors.

FIG. 25D shows a method 2500 d of determining noise estimates, accordingto one illustrated embodiment.

In particular, at 2540, the interrogation and detection systemdetermines an average noise estimate based on averaging of measures orsamples from all antennas or antenna channels other than the respectiveantenna or antenna channel for which the noise estimate will provide thecompensation factors. The averaging includes averaging of noisedetection portions which occur both before and after an interrogationportion of a transponder detection cycle. Such allows the interrogationand detection system to essentially determine whether the noise isconsistent, periodic, or non-random.

FIG. 25E shows a method 2500 e of determining noise estimates, accordingto one illustrated embodiment.

In particular, at 2550, the interrogation and detection systemdetermines an average noise estimate by determining a decomposed leastsquares average of noise measurements or samples. While a decomposedleast squares approach is illustrated, a wide variety of otherapproaches may be employed (e.g., Bayesian averaging).

FIG. 25F shows a method 2500 f of determining noise estimates, accordingto one illustrated embodiment.

In particular, at 2560, the interrogation and detection system comparesnoise measured from before an interrogation portion of the transponderdetection to noise measured after the interrogation portion of thetransponder detection cycle. A difference between the noise measurementsmay represent variation in noise. At 2562, the interrogation anddetection system may increase the sample averaging time for samplingresponses to interrogation signals if a determined difference (i.e.,variation in noise) is greater than a variation threshold. Such mayallow the interrogation and detection system to accommodate differentnoise sources, such as those that produce periodic or non-random versusthose that produce random noise.

FIG. 26A shows a measured or sampled response 2600 a, according to oneillustrated embodiment.

The response 2600 a in the time domain was measured in an environmentwhich contained a noise source (e.g., fluoroscope) but no transponder.The response 2600 a has not be subjected to noise cancellation oradjustment. The amplitude (Y-axis) is in mV, while the time (X-axis) isin μs.

FIG. 26B shows a measured or sampled response 2600 b, according to oneillustrated embodiment.

The response 2600 b is the response 2600 a having been subjected tonoise cancellation or adjustment. Most of the peaks have noticeably beendiminished.

FIG. 26C shows a measured or sampled response 2600 c, according to oneillustrated embodiment.

The response 2600 c is the response 2600 a after a fast Fouriertransformation to the frequency domain. The amplitude (Y-axis) is in mV,while the time (X-axis) is in frequency. There are three distinctivepeaks of noise.

FIG. 26D shows a measured or sampled response 2600 d, according to oneillustrated embodiment.

The response 2600 d is the noise cancelled response 2600 b after a fastFourier transformation to the frequency domain. The peaks have beennoticeable diminished, indicating that almost all noise has been removedby the noise cancellation.

FIG. 27A shows a sampled or measured response 2700 a, according to oneillustrated embodiment.

The response 2700 a in the time domain was measured in an environmentwhich contained a noise source (e.g., fluoroscope) and a transponder.The response 2700 a has not be subjected to noise cancellation oradjustment. The amplitude (Y-axis) is in mV, while the time (X-axis) isin μs.

FIG. 27B shows a measured or sampled response 2700 b, according to oneillustrated embodiment.

The response 2700 b is the response 2700 a after being subjected tonoise cancellation. While many the peaks (associated with noise) havenoticeably been diminished, other distinctive peaks remain.

FIG. 27C shows a measured or sampled response 2700 c, according to oneillustrated embodiment.

The response 2700 c is the response 2700 a after a fast Fouriertransformation to the frequency domain. The amplitude (Y-axis) is in mV,while the time (X-axis) is in frequency. There are three distinctivepeaks.

FIG. 27D shows a measured or sampled response 2700 d, according to oneillustrated embodiment.

The response 2700 d is the noise cancelled response 2700 b after a fastFourier transformation to the frequency domain. Two of the three peakshave been noticeable diminished, indicating that almost all noise hasbeen removed by the noise cancellation, and leaving a single distinctivepeak at the resonant frequency of the transponder.

The above described embodiments may improve a detection range versusnoise performance over other more conventional approaches. Theembodiment of the present disclosure may be capable of achieving farsuperior performance, having greater detection range in even mildlynoisy environments. Such is particularly advantageous in environmentssuch as operating theaters, and substantially helps reduce falsereadings (e.g., false positives, false negatives). Thus, such mayprovide the level of performance demanded by hospitals and doctors.

Thus, during each of a plurality of detection cycles, the interrogationand detection system performs a number of acts or operations. Theinterrogation and detection system receives unmodulated electromagneticsignals during a noise detection portion of the detection cycle.

The interrogation and detection system determines a noise valueindicative of a noise level that corresponds to a highest one of anumber N of samples or measurements of the unmodulated electromagneticsignals received during the noise detection portion of the detectioncycle, where the number N is greater than one. The interrogation anddetection system may determine a noise value indicative of a noise levelbased at least in part on the unmodulated electromagnetic signalsreceived during the noise detection portion of the detection cycle bysetting the noise value based on the highest one of six samples ormeasurements of the unmodulated electromagnetic signal received duringthe noise detection portion of the detection cycle. The interrogationand detection system adjusts a signal detection threshold based at leastin part on the determined noise value of at least one of the detectioncycles. The interrogation and detection system may adjust the signaldetection threshold by adjusting the signal detection threshold based atleast in part on a first number of determined noise values indicative ofa noise level during at least one noise detection portion that occurredbefore the receive response portion of a first one of the detectioncycles and a second number of determined noise values indicative of anoise level during at least one noise detection portion that occurredafter the receive response portion of the first one of the detectioncycles. The interrogation and detection system may adjust the signaldetection threshold based at least in part on the determined noise valueof at least one of the detection cycles by adjusting the signaldetection threshold to be approximately twice an average of at least oneof the first and the second number of determined noise values. Theinterrogation and detection system may, for example, adjust the signaldetection threshold based at least in part on the determined noise valueof at least one of the detection cycles by adjusting the signaldetection threshold to be approximately twice a greatest one of at leastone of the first and the second number of determined noise values.

The interrogation and detection system emits at least oneelectromagnetic interrogation signal during a transmit portion of thedetection cycle. The interrogation and detection system receivesunmodulated electromagnetic signals during a receive response portion ofthe detection cycle that follows the transmit portion of the detectioncycle.

The interrogation and detection system determines the presence orabsence of a transponder based at least in part on a number M of samplesor measurements of the unmodulated electromagnetic signals receivedduring the detection cycle and the adjusted signal detection threshold,where the number M is greater than one. A ratio of N:M may be at leastequal to 4. N may be equal to about 200 and M may be equal to about 800.For example, the interrogation and detection system may determine thepresence or absence of a transponder by comparing a maximum value of aplurality of matched filter outputs with the adjusted signal threshold.

In some embodiments, the interrogation and detection system determinesif an output of at least one matched filter during the noise detectionportion of the detection cycle exceeds a noise fault thresholdindicative of a noise fault. Such may be employed to prevent extraneousobjects (e.g., metal table, EKG leads, etc.) from producing a positiveresult. For example, the interrogation and detection system maydetermine if the output of the at least one matched filter during thenoise detection portion of the detection cycle exceeds the noise faultthreshold for a defined period of time. The interrogation and detectionsystem may then terminate the detection cycle in response to the outputof the at least one matched filter exceeding the noise fault thresholdfor the defined period of time.

The interrogation and detection system may convert the receivedsignal(s) from the time domain to the frequency domain spectrum. Suchmay be employed, for example in lieu of the match filtering. Theinterrogation and detection system may, for example, perform a Fouriertransform, for instance a fast Fourier transform such as a 256 pointfast Fourier transform. Suitable algorithms and/or sets of software codefor performing such are available or can be written. The interrogationand detection system may search the frequency domain spectrum todetermine the object with the strongest resonance in a defined frequencyband. For example, the interrogation and detection system may search thefrequency domain spectrum from about 120 KHz to about 175 KHz. Anamplitude of the resonant object may be computed as the sum of theresonant power plus and minus 2 fast Fourier transform bins from thepeak resonance frequency. This approach may provide a more accuratemeasurement of power than simply using the peak value. The frequency ofthe resonant object may be computed using an interpolation approach.This approach may provide a more accurate determination of resonantfrequency than simply using the fast Fourier bin number. Theinterrogation and detection system may determine the presence or absenceof a transponder based at least in part on a frequency of theunmodulated electromagnetic signals received during the detection cyclebeing within a defined frequency range. The defined frequency range mayextend from about 137 KHz to about 160 KHz.

The interrogation and detection system may ignore any unmodulatedelectromagnetic signals received during a recovery portion (if any) ofthe detection cycle that precedes the receive response portion of thedetection cycle. Such may be useful in preventing false positives (i.e.,tag detections) from being triggered by the transmission of theinterrogation or excitement signals.

The interrogation and detection system may determine a Q value (i.e.,Quality factor) of the resonant object from a signal decay slope for thereceived unmodulated electromagnetic signal(s) returned by the resonantobject. For example, the interrogation and detection system maydetermine a Q value of the unmodulated electromagnetic signals receivedduring the detection cycle being at least equal to a threshold Q value.The threshold Q value may, for example, be 35. The interrogation anddetection system may, for example, use multiple windows, for instancefive (5) window positions may provide suitable results. Theinterrogation and detection system may determine the presence or absenceof a transponder based at least in part on a Q value of the unmodulatedelectromagnetic signal(s) received during the detection cycle. Theinterrogation and detection system may preferably employ the Q valuedetermination in conjunction with determination based on the frequencyand on the determination based on the adjusted signal detectionthreshold.

Consequently, in some embodiments the tag detection may advantageouslybe based on the received unmodulated electromagnetic signal(s)satisfying all three conditions: 1) measured amplitude is above athreshold, which may be an adjustable threshold, 2) measured frequencyis between a lower limit and an upper limit, and 3) measured Q value isabove a minimum Q threshold. Interference, for example from RFID tags orEKG cables, are rejected when any of the following three conditions aresatisfied: a) measured frequency is below the lower frequency limit, b)measured frequency is above the upper frequency limit, or c) measured Qvalue is below the threshold Q value. Such may provided significantlysuperior results over previous approaches, preventing false positiveswhich could otherwise cause a patient to remain open for longer periodof time during surgery and tie up hospital personnel and resources.

The above description of illustrated embodiments, particularly the useof multiple antennas, the pulsed wide band frequency hopping withdynamic adjustment of the transmission frequency in the variousfrequency bands and the use of switched capacitors to achieve such,advantageously permit the use of inexpensive transponders which are notaccurately tuned to a chosen or selected resonant frequency. This is inmarked contrast to the approach typically taken with other types ofresonant transponders (i.e., transponders without memory). Suchapproaches typically interrogate or excite the resonant transponderusing narrow frequency bands centered closely on specific frequencies,to achieve a selected resonant response from a highly accuratetransponder in order to differentiate signal from noise. This is also inmarked contrast to the approach typically taken with radio frequencyidentification (RFID) tags whether active or passive, which alsotypically employ are narrow band to achieve a selected response from ahighly accurate RFID tag.

The interrogation and detection system herein described may furtherimplement a handheld wand 2802 as illustrated in FIG. 28. Wand 2802comprises a loop antenna 2806, a handle 2808, and a cord 2810. The wand2802 may be configured to interface with the interrogation and detectionsystem. The wand 2802 may be connected to the controller 18 by means ofthe chord 2810. The wand 2802 may be waved over the patient on thepatient support structure 26 while emitting an interrogation signal toexcite any transponder 24 which may be in or near the patient. Theantennas 16 a-16 f may then all be used to detect a signal from thetransponder as previously described. In one embodiment the controller 18controls the wand 2802. In one embodiment the wand 2802 emits aninterrogation signal and monitors for a response from a transponder 24.In one embodiment the wand 2802 operates independent of the antennas 16and the controller 18. In one embodiment the wand 2802 is wirelesslyoperated. In one embodiment the wand 2802 only detects a transponder anddoes not emit an interrogation signal. Many other implementations of thewand 2802 will be apparent to those of skill in the art in light of theillustrated embodiments. For example, the wand 2802 may be implementedin a form other than a loop antenna. The illustrated embodiments aregiven only by way of non-limiting example.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other transponders andinterrogation and detection systems, not necessarily the exemplarysurgical object transponders and interrogation and detection systemsgenerally described above.

For instance, the foregoing detailed description has set forth variousembodiments of the devices and/or processes via the use of blockdiagrams, schematics, and examples. Insofar as such block diagrams,schematics, and examples contain one or more functions and/oroperations, it will be understood by those skilled in the art that eachfunction and/or operation within such block diagrams, flowcharts, orexamples can be implemented, individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. In one embodiment, the present subject matter may beimplemented via Application Specific Integrated Circuits (ASICs).However, those skilled in the art will recognize that the embodimentsdisclosed herein, in whole or in part, can be equivalently implementedin standard integrated circuits, as one or more computer programsrunning on one or more computers (e.g., as one or more programs runningon one or more computer systems), as one or more programs running on oneor more controllers (e.g., microcontrollers) as one or more programsrunning on one or more processors (e.g., microprocessors), as firmware,or as virtually any combination thereof, and that designing thecircuitry and/or writing the code for the software and or firmware wouldbe well within the skill of one of ordinary skill in the art in light ofthis disclosure.

In addition, those skilled in the art will appreciate that themechanisms of taught herein are capable of being distributed as aprogram product in a variety of forms, and that an illustrativeembodiment applies equally regardless of the particular type of physicalsignal bearing media used to actually carry out the distribution.Examples of signal bearing media include, but are not limited to, thefollowing: recordable type media such as floppy disks, hard disk drives,CD ROMs, digital tape, and computer memory.

The various embodiments described above can be combined to providefurther embodiments. To the extent not inconsistent with the teachingsherein, all U.S. patents, U.S. patent application publications, U.S.patent applications, foreign patents, foreign patent applications andnon-patent publications commonly owned with this patent application andreferred to in this specification and/or listed in the Application DataSheet including: U.S. Patent Publication No. US 2004/0250819, publishedDec. 16, 2004; U.S. Provisional Patent Application No. 60/811,376 filedJun. 6, 2006; U.S. Provisional Patent Application No. 61/109,104 filedOct. 28, 2008; U.S. Provisional Patent Application No. 61/222,443 filedJul. 1, 2009; U.S. Provisional Patent Application No. 61/222,847 filedJul. 2, 2009; U.S. Provisional Patent Application No. 61/242,699, filedSep. 15, 2009; U.S. provisional patent application Ser. No. 61/242,704filed Sep. 15, 2009; U.S. Non-Provisional patent application Ser. No.11/743,104 filed May 1, 2007; U.S. Non-Provisional patent applicationSer. No. 12/472,199 filed May 26, 2009; U.S. Non-Provisional patentapplication Ser. No. 12/473,059 filed May 27, 2009; and U.S. Pat. No.6,026,818, issued Feb. 22, 2000, are incorporated herein by reference,in their entirety. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An apparatus to detect transponder taggedobjects which are used in performing medical procedures, the apparatuscomprising: a plurality of antennas spaced at fixed positions along atleast a portion of a length of a patient support structure that is sizedto support a patient, at least one of the antennas having a measurablephysical characteristic that varies in response to a physical forceapplied to the at least one of the antennas; and a control systemcommunicatively coupled to the antennas to activate respective ones ofat least two of the antennas to transmit respective interrogationsignals, to detect a response signal generated by a transponderresponsive to the interrogation signals, and to detect a valueindicative of the measurable physical characteristic that varies inresponse to the physical force applied to the at least one of theantenna.
 2. The apparatus of claim 1 wherein the measurable physicalcharacteristic that varies in response to a physical force applied tothe at least one of the antennas is a resistance of the antenna, whichindicates an amount of strain at the position of the antenna on thepatient support structure.
 3. The apparatus of claim 1 wherein a numberof the plurality of antennas are electrically coupled in at least onebridge configuration.
 4. The apparatus of claim 3 wherein the at leastone bridge configuration is a Wheatstone bridge configuration.
 5. Theapparatus of claim 1 wherein the control system further provides analert in response to the measurable physical characteristic exceeding athreshold value.
 6. The apparatus of claim 5 wherein the control systemfurther provides an indication of a location on the patient supportstructure where the measurable physical characteristic has exceeded thethreshold value.
 7. The apparatus of claim 1 wherein the valueindicative of the measurable physical characteristic is indicative of atleast one of an amount of strain, an amount of force or an amount ofpressure.
 8. The apparatus of claim 1 wherein the patient supportstructure comprises a surgical table or a bed.
 9. The apparatus of claim1 wherein the control system sequentially activates respective ones ofthe antennas to transmit respective interrogation signals and detectsvia the antennas other than a most recently activated one of theantennas the response signal generated by the transponder responsive toa most recent one of the interrogation signals.
 10. A method to detecttransponder tagged objects which are used in performing medicalprocedures, the method comprising: for a plurality of antennas spaced atfixed positions along at least a portion of a length of a patientsupport structure that is sized to support a patient, activatingrespective ones of at least two of the antennas to transmit respectiveinterrogation signals, detecting through the antennas a response signalgenerated by a transponder responsive to the interrogation signals, anddetecting a measurable physical characteristic that varies in responseto a physical force applied to at least one of the plurality ofantennas.
 11. The method of claim 10 wherein detecting a measurablephysical characteristic that varies in response to a physical forceapplied to the at least one of the plurality of antennas comprisesdetecting a change in a resistance of each antenna.
 12. The method ofclaim 10 further comprising providing an alert in response to a value ofthe detected measurable physical characteristic equaling or exceeding athreshold value.
 13. The method of claim 12 further comprising providingan indication of a location on the patient support structure where thevalue of the detected measurable physical characteristic has equaled orexceeded the threshold value.
 14. The method of claim 10 whereindetecting a measurable physical characteristic that varies in responseto a physical force applied to the at least one of the plurality ofantennas comprises detecting a physical characteristic indicative of atleast one of a strain, a force or a pressure applied to the antenna. 15.The method of claim 10 wherein activating respective ones of at leasttwo of the antennas to transmit respective interrogation signals anddetecting through the antennas a response signal generated by atransponder responsive to the interrogation signals comprisessequentially activating respective ones of the antennas to transmitrespective interrogation signals and detecting via the antennas otherthan a most recently activated one of the antennas the response signalgenerated by the transponder responsive to a most recent one of theinterrogation signals.